Sinclair had a disastrous final few minutes for Wrexham
A Glenn Poole penalty in a dramatic finish saved a point for AFC Wimbledon.
Wrexham goalkeeper Chris Maxwell saved Danny Kedwell's early penalty then saw Dons stopper James Pullen net an own goal from Paul Lorraine's clearance.
Brett Johnson's header was turned into his own net by Frank Sinclair for a 90th-minute equaliser, but Andy Mangan struck in stoppage time for Wrexham.
Sinclair was sent off for bringing down Kedwell in the area, with Poole scoring to keep alive the Dons' play-off hopes.
Wrexham manager Dean Saunders: "I don't know what to say... we've weathered the storm first half after a difficult trip here. Christian Smith gave away a ridiculous penalty but Chris Maxwell's saved it and we got through.
"Second half we came out and we've scored, I felt quite comfortable.
"Three minutes to go they scored I've never seen anything like it, you couldn't write what's happening to us at the moment.
"There's 10 seconds left on the clock, Curtis [Obeng] can do anything but what he's done.
"He's only got to clear it and he turns and gives it to the keeper, they win a corner and get the penalty.
"I don't know what's happened in the box apparently the lad's thrown a punch at Frank [Sinclair], he's retaliated and been sent off.
"That's typical of what's been happening with us. I thought we'd won it twice.
"I was 10 seconds away from saying congratulations to everybody and one decision from Curtis has cost everyone."
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