Brechin attacked from the start and in the opening minute a shot from James Sharp flew across the face of goal. After 16 minutes a Charlie King free-kick was just missed by both James Sharp and Scott Walker.
Ayr threatened for the first time after 22 minutes when Andrew Ferguson crossed for Scott Chaplin whose header was saved by Craig Nelson.
Brechin were out of luck in the 27th minute when Sharp laid the ball off to King, and his chip came back off the cross bar.
Brechin took the lead after 43 minutes when a linesman spotted a hand-ball in the Ayr box. Ayr's Marc Smith was booked and Paul Ritchie scored from the spot.
Brechin stretched their lead two minutes into the second half when the ball broke off Steven Hampshire for Graham Gibson to score with a shot on the turn. Walker headed just over as Brechin looked for more goals. Then Ritchie had a header deflected for a corner.
Ayr went close after 59 minutes when Richard Buckley had a header saved by Nelson. After 76 minutes it was Ayr's turn to be out of luck when a shot from Ferguson came back off the Brechin post.
Play was end to end in the closing stages, and King had a shot saved after a solo run. Then at the other end Willy Lyle shot into the side netting.
Brechin wrapped things up a minute into stoppage time when a superb flick from King released Hampshire, and he supplied a fine finish.