The Buddies were deservedly two ahead on the stroke of half-time when Dargo broke clear to score.
Mark Roberts ensured a tight finish with a successful 58th-minute penalty after Darren McGregor handled.
Dargo had returned to the St Mirren starting line-up along with David van Zanten as Paddy Cregg missed out through injury and Jure Travner dropping to the bench.
Ayr's personnel problems meant that Ross Robertson, Stuart Bannigan and Chris Smith started in the absence of the injured Willie Easton, cup-tied Michael Moffat and suspended Alan Trouten.
And the restructured home defence was breached early on as Michael Higdon chested the ball into the path of van Zanten and, when the defender's pass found Dargo, the striker curled a low drive through his marker's legs from 20 yards and inside the near post.
McGregor loped forward before slicing well wide and Paul McGowan tried a snap shot from just outside the area without troubling goalkeeper David Crawford as the Buddies looked to build on that lead.
Somerset Park's tight terracing can be an intimidating arena on big occasions, but St Mirren's early dominance had the home support all but silenced.
Bannigan attempted to lift their spirits after being sent into the penalty box following a clever Ryan McCann run, but the forward's audacious attempt from an almost impossible angle struck the outside of the post and wide.
Higdon was lucky to escape with only a yellow card after a lunging tackle that left Ayr defender Eddie Malone requiring treatment.
Just as Ayr began to exert some pressure in the dying seconds of the first half, St Mirren extended their lead.
As Higdon was tackled on the halfway line, the ball spun off the striker and behind the home defence, where Dargo raced clear, rounded the goalkeeper then outfoxed two defenders as he turned back towards what was now a gaping goalmouth to score.
It looked like St Mirren were going to finish off the Ayr challenge when Dargo twice squandered chances to complete his hat-trick.
However, he sent a low drive just past the far post after being put clear by Higdon's flick-on and then sliced another well wide.
Higdon sent a powerful header into the arms of Crawford, but Ayr survived before pulling a goal back after a spell of pressure of their own.
A McCann drive was deflected for a corner and, when the ball was swung in, it struck the arm of defender McGregor.
Roberts, the hero of the previous round's replay victory over Hibs, sent goalkeeper Paul Gallagher the wrong way from the penalty spot.
Ayr pushed for a winner against an increasingly nervy Paisley side, but it was the visitors' McGowan who was next to threaten with a 16-yard drive saved by Crawford at the second attempt.
A ball over the top from Roberts found Robertson, but the young Ayr man could only get enough of his big toe on the ball to turn it straight into Gallagher's arms and St Mirren survived to secure a quarter-final place.
Live text and stats ?
Saturday, 5 February 2011
Scottish Cup
Home Team
Score
Away Team
Time
Ayr
1-2
St Mirren
FT
(HT 0-2)
Roberts (pen) 58
Dargo 7
Dargo 45+1
Ayr
01?Crawford
03?Malone
05?Campbell
07?Robertson
11?Smith
02?Tiffoney
04?Lauchlan
08?McLaughlin
09?Bannigan
06?McCann yellow card
10?Roberts
Substitutes
20?McWilliams,
12?Woodburn,
14?Shaun Kelly,
16?Paterson,
15?Dale Moore
St Mirren
01?Gallacher
02?van Zanten
05?Mair
06?Potter
14?McGregor
17?McAusland
08?Thomson
11?Goodwin yellow card
09?Dargo (Mclean 75)
10?Higdon yellow card (Mooy 90+2)
19?McGowan (Murray 81)
Substitutes
12?Samson,
16?Travner,
07?Murray,
33?Mooy ,
45?Mclean
Ref:?NorrisAtt:?5,997
AYR ST MIRREN
Possession
Ayr 53%
St Mirren 47%
Attempts on target
Ayr 5
St Mirren 7
Attempts off target
Ayr 3
St Mirren 7
Corners
Ayr 3
St Mirren 4
Fouls
Ayr 9
St Mirren 17
Final Result
Full Time
90:00+2:50 The referee signals the end of the game.
90:00+1:11 Substitution (St Mirren) makes a substitution, with Aaron Mooy coming on for Michael Higdon.
89:25 Foul by Lee Mair on Jonathan Tiffoney, free kick awarded. Strike on goal comes in from Scott McLaughlin from the free kick,
save by Paul Gallacher.
87:13 Hugh Murray crosses the ball, Martyn Campbell gets a block in.
84:56 Steven Thomson fouled by Stuart Bannigan, the ref awards a free kick. Paul Gallacher takes the free kick.
84:29 Free kick awarded for a foul by Hugh Murray on Scott McLaughlin. Free kick taken by Scott McLaughlin.
84:10 Marc McAusland delivers the ball, Martyn Campbell makes a clearance.
82:22 Ebbie Malone sends in a cross, clearance made by Darren McGregor.
81:34 Ryan McCann delivers the ball, John Potter makes a clearance.
80:35 Scott McLaughlin has an effort at goal from just outside the box which goes wide of the right-hand post.
80:35 Substitution Paul McGowan goes off and Hugh Murray comes on.
79:56 Foul by John Potter on Mark Roberts, free kick awarded. Scott McLaughlin takes the direct free kick.
79:26 Effort from 12 yards by Ross Robertson. Save by Paul Gallacher.
79:16 Centre by Scott McLaughlin, clearance by Darren McGregor.
78:14 Paul McGowan takes a shot. Save by David Crawford.
76:42 Paul McGowan takes a shot. David Crawford makes a comfortable save.
76:33 The ball is delivered by Kenneth McLean, Martyn Campbell makes a clearance.
74:46 Substitution Kenneth McLean is brought on as a substitute for Craig Dargo.
73:46 Scott McLaughlin takes a shot. Blocked by Lee Mair. Inswinging corner taken by Scott McLaughlin.
72:17 The official flags Michael Higdon offside. Jim Lauchlan takes the free kick.
71:58 Michael Higdon takes a shot. David Crawford makes a comfortable save.
71:20 The ball is crossed by Jonathan Tiffoney, save made by Paul Gallacher.
70:48 Steven Thomson challenges Ryan McCann unfairly and gives away a free kick. Ebbie Malone restarts play with the free kick.
69:00 Jim Lauchlan fouled by Michael Higdon, the ref awards a free kick. Direct free kick taken by David Crawford.
68:30 Martyn Campbell gives away a free kick for an unfair challenge on John Potter. Paul Gallacher takes the free kick.
67:46 Jonathan Tiffoney fouled by Paul McGowan, the ref awards a free kick. Scott McLaughlin crosses the ball from the free kick
left-footed from right wing, Paul Gallacher makes a clearance.
67:12 Craig Dargo is ruled offside. Free kick taken by Jim Lauchlan.
66:22 Unfair challenge on Michael Higdon by Martyn Campbell results in a free kick. Jim Goodwin takes the free kick.
65:50 The offside flag is raised against Michael Higdon. David Crawford takes the free kick.
Correction - 64:57 The referee blows for offside. Paul Gallacher takes the free kick.
64:57 Stuart Bannigan is flagged offside by the assistant referee. Free kick taken by Paul Gallacher.
62:55 Craig Dargo concedes a free kick for a foul on Jonathan Tiffoney. Direct free kick taken by David Crawford.
59:41 The assistant referee flags for offside against Craig Dargo. Indirect free kick taken by Jim Lauchlan.
58:08 Outswinging corner taken right-footed by Craig Dargo from the right by-line, Jim Lauchlan makes a clearance.
57:27 Centre by Stuart Bannigan, Ryan McCann takes a shot. Blocked by Lee Mair. Inswinging corner taken by Scott McLaughlin. The
referee penalises Darren McGregor for handball.
57:27 GOAL - Mark Roberts:Ayr 1 - 2 St Mirren Penalty scored by Mark Roberts. Ayr 1-2 St Mirren.
55:16 The ball is sent over by Paul McGowan, Michael Higdon takes a shot. Save by David Crawford.
53:40 Centre by Paul McGowan, Craig Dargo has an effort at goal from just inside the box that misses to the right of the goal.
52:28 Craig Dargo crosses the ball, blocked by Martyn Campbell. Inswinging corner taken right-footed by Paul McGowan from the right
by-line, Jonathan Tiffoney fouled by Darren McGregor, the ref awards a free kick. David Crawford takes the direct free kick.
51:10 The offside flag is raised against Craig Dargo. David Crawford takes the indirect free kick.
50:33 Mark Roberts takes a shot. Save by Paul Gallacher.
49:30 Shot by Craig Dargo from deep inside the penalty area misses to the right of the goal.
48:19 The ball is crossed by Chris Smith, clearance by Craig Dargo.
46:34 Steven Thomson takes a shot. David Crawford makes a comfortable save.
45:01 The referee gets the second half started.
Half Time
45:00+1:58 The players leave the pitch at half time.
45:00+1:00 GOAL - Craig Dargo:Ayr 0 - 2 St Mirren Craig Dargo finds the back of the net with a goal from inside the box to the bottom right corner of the goal. Ayr 0-2 St Mirren.
44:32 Craig Dargo concedes a free kick for a foul on Jonathan Tiffoney. Direct free kick taken by Scott McLaughlin.
43:03 Mark Roberts produces a cross, clearance made by Darren McGregor. Corner taken by Scott McLaughlin from the left by-line,
Header on goal by Chris Smith from inside the box goes harmlessly over the target.
42:00 The offside flag is raised against Mark Roberts. Paul Gallacher restarts play with the free kick.
39:58 Paul McGowan has an effort at goal from deep inside the area missing to the right of the goal.
38:07 Free kick awarded for an unfair challenge on Michael Higdon by Jim Lauchlan. Jim Goodwin restarts play with the free kick.
Martyn Campbell fouled by Michael Higdon, the ref awards a free kick. David Crawford takes the direct free kick.
35:55 A cross is delivered by Marc McAusland, Header by Michael Higdon from deep inside the penalty area misses to the left of the
target.
35:06 Jim Lauchlan concedes a free kick for a foul on Michael Higdon. Marc McAusland restarts play with the free kick.
33:15 Foul by Michael Higdon on Ebbie Malone, free kick awarded. David Crawford takes the direct free kick.
33:15 Booking The referee books Michael Higdon for unsporting behaviour.
32:36 Ross Robertson concedes a free kick for a foul on Jim Goodwin. Paul Gallacher takes the free kick.
30:24 The ball is crossed by David van Zanten.
29:28 Lee Mair crosses the ball, Jonathan Tiffoney makes a clearance. Inswinging corner taken by Steven Thomson, clearance by Mark
Roberts.
28:32 Marc McAusland crosses the ball, Martyn Campbell fouled by Michael Higdon, the ref awards a free kick. Direct free kick taken
by David Crawford.
26:56 The ball is swung over by Stuart Bannigan.
25:28 The ball is sent over by Stuart Bannigan, John Potter makes a clearance.
24:14 Jim Goodwin concedes a free kick for a foul on Ryan McCann. Jim Lauchlan restarts play with the free kick.
24:14 Booking Jim Goodwin is booked.
19:32 Paul McGowan fouled by Jonathan Tiffoney, the ref awards a free kick. Jim Goodwin takes the free kick.
17:48 Free kick awarded for an unfair challenge on Martyn Campbell by Craig Dargo. Free kick taken by Jim Lauchlan.
14:12 Darren McGregor gives away a free kick for an unfair challenge on Mark Roberts. Scott McLaughlin crosses the ball in from
the free kick, save made by Paul Gallacher.
13:00 Paul McGowan has an effort at goal from outside the area which misses left.
11:10 Darren McGregor produces a left-footed shot from deep inside the penalty box which goes wide of the left-hand upright.
10:04 Centre by Jonathan Tiffoney, Header from close in by Mark Roberts misses to the right of the goal.
8:47 Craig Dargo produces a cross, Martyn Campbell gets a block in. Corner taken by Steven Thomson from the right by-line, Jim
Goodwin takes a shot. Blocked by Jim Lauchlan.
7:39 Foul by Ryan McCann on Darren McGregor, free kick awarded. Paul Gallacher takes the direct free kick.
7:39 Booking Ryan McCann booked for unsporting behaviour.
6:19 Michael Higdon provided the assist for the goal.
6:19 GOAL - Craig Dargo:Ayr 0 - 1 St Mirren Craig Dargo finds the back of the net with a goal from just outside the box to the bottom left corner of the goal. Ayr 0-1
St Mirren.
3:24 Foul by Ross Robertson on Lee Mair, free kick awarded. Direct free kick taken by Paul Gallacher.
2:53 The referee penalises Marc McAusland for handball. Jim Lauchlan takes the free kick.
0:55 Jonathan Tiffoney fouled by David van Zanten, the ref awards a free kick. Direct free kick taken by Ebbie Malone.
0:20 Craig Dargo challenges Jim Lauchlan unfairly and gives away a free kick. Free kick taken by David Crawford.
0:00 The game gets underway.
Live text and data provided by The Press Association.
Source: BBC Sport
Source: BBC Sport