Declan McDaid curls in the only goal of the game at East End Park
Ayr United moved back up to third in the Championship thanks to a lovely curling effort from Declan McDaid at East End Park.
Lawrence Shankland was twice denied by Dunfermline goalkeeper Ryan Scully as the visitors sought a second goal.
Dunfermline rallied, with Danny Devine and Louis Longridge going close before Bruce Anderson blasted a last-minute chance over the crossbar.
Ayr are now nine points behind Dundee United with two games in hand.
Dunfermline remain fifth, four points behind Inverness Caley Thistle, after back-to-back home defeats.
Ian McCall's visitors had gone into the match on the back of a poor run, with just one win in six games, but they dominated the first hour in Fife.
The only goal arrived on 31 minutes with McDaid swing a shot into the right-hand side of the net from the left of the box.
Shankland shot straight at Scully just before half-time and was later denied by the keeper in a one-on-one situation.
Dunfermline had chances to rescue a point, with Devine shooting over from a Faissal El Bakhtaoui flick-on, while Longridge had two shots stopped by Ross Doohan before Anderson's glaring late miss.
'A big win for Ayr United'
Ayr United manager Ian McCall: "That was a big win for us - it was a very nervous last five minutes but I don't think anyone would say we didn't deserve to win. I'm disappointed we weren't three or four goals ahead at that point.
"There was one clear chance for Dunfermline at the end but it would've been a travesty if we hadn't taken all three points.
"If we can make the play-offs, that would be fantastic. We go again on Tuesday night against Morton, which will be tough."
Dunfermline manager Stevie Crawford: "It's bitterly disappointing. There's a way of losing football, our first half was unacceptable. They came and dominated. I'm not pointing the finger but collectively they outdid us.
"If you don't work hard enough or do jobs properly you get punished. We didn't get the rub of the green but the first half performance wasn't good enough."
