Palace thought they were hanging onto a 2-1 lead when Ouattara headed home in the 88th minute from Michael Kayode's long throw, after Sepp van den Berg flicked it on cleverly.
It was previously the Adam Wharton show, as the Palace midfielder's first goal for the club put them on cruise control in west London.
The England midfielder had gone 93 games without a goal for the Eagles but his drive that went through Brentford goalkeeper Caoimihn Kelleher looked to have settled the London derby contest in west London.
His cartwheel and somersault celebration made it a goal worth waiting for but Ouattara was on hand again late on for the Bees to ensure they took a point.
Wharton's earlier strike was part of a poor day for Bees goalkeeper Kelleher, who conceded an early penalty by tripping Ismalia Sarr after just a few minutes.
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Referee Sam Barrott - who wrongly ruled out an Eberechi Eze free-kick goal in this fixture last season - initially gave a corner, but was sent to the monitor to overturn the decision.
Sarr converted his 21st goal of the season, matching Andy Johnson's Palace record for most goals in all competitions during a Premier League campaign.
Palace should have been further ahead as Sarr and then Jorgen Strand Larsen hit the post - before Brentford equalised in fortunate circumstances.
Yehor Yarmoliuk's cross was cleared by Jaydee Canvot into Ouattara's head - the Brentford striker knew nothing about it as the ball then flew into the net.
But Palace - through their midfield maestro Wharton - were back ahead early in the second half as Wharton struck from the edge of the area via Kelleher's mistake.
Brentford tried to find a way back in but Palace were relatively comfortable. That was until Ouattara's late leveller - which preceded a whopping TEN minutes of stoppage time.
The Bees nearly won it as both Kevin Schade and Igor Thiago blazed efforts over the bar from inside the box - as the spoils were shared.
The result is a slight disappointment for Brentford after Manchester City winning the FA Cup on Saturday meant eighth place is now a European spot. The Bees still hold onto that position, but will lose it ahead of the final day trip to Liverpool if Chelsea beat Tottenham on Tuesday, live on Sky Sports.
Brentford will probably have to beat Liverpool - in Mohamed Salah's farewell match on the final day - to stand a chance of Europe.
More to follow...
