Goals from James McAtee and Iliman Ndiaye had United seemingly in control of the game, before Jerry Yates dragged the visitors on level terms before the break.
Charlie Patino put them ahead in the second half but the visitors had both Marvin Ekpiteta and Dominic Thompson sent off for two yellow cards.
United had two goals chalked off for offside and missed a penalty before eventually finding the equaliser deep into eight minutes of injury time, Ollie Norwood volleying home from outside the area.
There was still time for one more excellent Blackpool chance, former Blade CJ Hamilton racing clear before failing to get good connection on his shot, and both Wes Foderingham and Shayne Lavery were shown red cards after the final whistle after a coming-together at full-time.
Here’s how we tried our best to rate United’s players on an up-and-down afternoon full of late drama at the Lane...
1. Wes Foderingham 4
Left horribly exposed for two of Blackpool's three goals and could do little about the other, either, as Yates directed his header back across the United goalkeeper and in. Otherwise had little to do before he became embroiled in a post-match spat with Lavery and saw red, meaning he'll miss another chunk of games at a key time Photo: Simon Bellis
2. George Baldock 4
Back in the side after his absence with a side strain, Baldock lacked no effort down the right but his final ball was at times frustrating for those in the middle after he had worked his way into good positions. Came off late on for Khadra but judging by the way he sprinted to the touchline it was more tactical than injury-related Photo: Simon Bellis
3. Chris Basham 5
Continued in defence despite Ahmedhodzic being fit enough to take his place on the bench and was inches away from an equaliser late in the game as he came flying in but just couldn't stretch enough to meet Doyle's wicked cross. Photo: Simon Bellis
4. John Egan 4
Was unfortunate for Blackpool's third as he cut out a dangerous through-pass but could only steer it into the path of Dougall to score past Foderingham. Ninety-nine times out of 100, that goes to safety. Turned attacker soon after in a bid to make amends after racing forwards with the ball but his shot was blocked. Half the ground thought he had equalised later on but he could only hit the side-netting. Photo: Andrew Yates