Hibernian's winless run stretched to seven games as St Mirren levelled in the 91st minute to share the points in the Scottish Premiership.
Following the disappointing League Cup semi-final defeat by 10-man Aberdeen at the weekend, Hibs initially roared back thanks to Josh Campbell's skimmed effort in the 12th minute.
Mark O'Hara's penalty - which was disputed by Hibs head coach Nick Montgomery - levelled the score after the break, before Joe Newell thought he had given Hibs the winner after tapping in a fantastic flowing move.
But young striker Lewis Jamieson scored his first goal for St Mirren in added time to epitomise the Buddies' fightback.
"If that's a penalty, there's going to be 10 penalties every game," Montgomery said of Jordan Obita's foul on Richard Taylor.
"A 6ft 5in player falls to the ground with minimal contact. I'm looking forward to getting some decisions moving forward.
"Every time we score two goals, we seem to concede two, and that's something we need to change."
St Mirren move five points behind second-placed Rangers, with Hibs jumping one place to eighth.
Montgomery's side seemed to respond brilliantly to the despondency of the weekend, when they largely dominated Aberdeen but still tasted defeat at Hampden.
They flew out the blocks, but their opening goal was still courtesy of a gift from St Mirren. The normally reliable Alex Gogic let the ball roll under his foot as he collected a pass, allowing Dylan Vente to square to Campbell, whose unorthodox shot found the bottom corner.
During a frantic spell, four Hibs players shot consecutively before St Mirren cleared, but that was about it for their first-half chances.
The hosts started to come back into the game in the final five minutes of the half - and they continued after the break in the same vein before they were similarly gifted a chance at goal.
A corner to the front post resulted in a penalty for a foul in the middle, where Jordan Obita had pulled Richard Taylor's shirt. Midfielder O'Hara stepped up and finished with his usual aplomb.
Another Gogic mistake allowed Elie Youan clear through on goal. The Frenchman tried to round the goalkeeper, but Zach Hemming made a vital save.
Hibs were not done yet. Newell got on to the end of a free-flowing move to tap in and send the away end doolally, but they would not go home happy.
Jamieson was brought on as a late substitute and picked the perfect time to score his first St Mirren goal, firing in the equaliser with his second bite of the cherry.
Player of the Match - Joe Newell (Hibernian)
Same old Hibs, uncharacteristic St Mirren - analysis
Montgomery spoke pre-game about turning draws into wins. Yet again, they impressed with the performance, but the result did not follow.
They passed the ball with confidence, they did not allow St Mirren to play virtually any football for the first 35 minutes, they looked dangerous with Youan and Jair Tavares.
But it was not enough. That is now two wins in 10 games for Montgomery and what looked like a decent start has turned into a very slow one.
St Mirren began as poorly as they have all season but still managed to come back and rescue something. In a game of mentalities, St Mirren showed theirs is far stronger.
It is an encouraging sign when you can get something when you are not at your best. Manager Stephen Robinson can take the positive from that.
What they said
St Mirren manager Stephen Robinson: "I thought the boys were terrific. One of our best performances of the season against a very good Hibs side. We got done by a mistake. We dominated large spells of the game but couldn't find the finish. Our end product wasn't quite there.
"It was young LJ [Lewis Jamieson], I'm delighted for him. He's a talented boy and I have a lot of faith in him. He's rewarded me with a very good equaliser.
Hibernian head coach Nick Montgomery: "A lot of frustration. Another game we were ahead in away from home. I thought we should have been smart enough to get out of game.
"We've been talking about managing games a lot. That's the disappointing thing. They were a lot of positives to take out of that. First-half, I thought we were outstanding."
St Mirren visit Dundee on Saturday, while Hibs host Kilmarnock at the same time (both 15:00 GMT).