Veteran keeper Jamie MacDonald was Raith's penalty hero as Ayr were denied all three points in Fife.
The 36-year-old thrwarted Ben Dempsey from the spot as United missed another chance to make key ground at the top of the Championship.
And they were forced to settle for a share of the goalless spoils in Kirkcaldy on a night where defences won out.
Lee Bullen made three changes to the side beaten by Partick last week as Reece McAlear, Mark McKenzie and Daire O'Connor all came in for starts with Paul Smith, Fraser Bryden and Jayden-Mitchell Lawson missing out.
And after a tight start, it was United who went closest to the opener when McAlear played in Dipo Akinyemi to shoot just over.
Ayr then survived shouts for a penalty when the ball struck Nick McAllister's arm in the box, but ref Colin Steven remained unmoved.
And the lively Dylan Easton went close midway through the first half when cutting inside to fire just wide from the angle of the box.
The game then slowed to something of a war of attrition as both sides struggled to create clearcut chances before the interval.
But Ayr finished the half with their tails up Dempsey was denied from point blank range and United started the second half in similar fashion.
And they won an early spot kick after the restart when O'Connor and McKenzie combined to earn the award.
However, Dempsey was this time denied from 12 yards as MacDonald threw himself to his left to make the save.
Easton fired a looping effort inches over as Rovers tried to rub salt in the wounds with the game opening up.
Ayr sent new signing Chris Maguire into the fray for the final 20 minutes as they looked to turn their increasing dominance of the ball into a winner.
And his guile was clear to see as United pinned back the hosts in the closing stages.
Akinyemi planted a free header wide in the final minute as Ayr poured forward but they couldn't force the winner their pressure deserved.
