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The Blades were beaten 2-1 in the play-off final by Sunderland, with Tom Watson's goal in the fifth minute of second-half stoppage time snatching promotion. 

United had taken the lead in the 25th minute through Tyrese Campbell, but was pegged back with 14 minutes to play by Eliezer Mayenda's fierce finish into the roof of the net. 

But after a poor pass by Kieffer Moore, Watson was allowed time and space to run at the Blades' defence before curling an inch-perfect strike past Michael Cooper. 

Indeed, the 19 year-old's match-winning moment was the latest goal in a second-tier play-off final in normal time on record (since 2004-2005), though Wilder said it was avoidable. 

Anel Ahemedhodzic was off the field injured when Watson struck, with the winner just the Black Cats' third shot on target for the duration of the contest at Wembley Stadium. 

"You've got to put teams to bed, and you've got to be clinical, and you've got to be tidy, and you've got to be smarter," Wilder said.

"We weren't smart in terms of our organisation on the second goal. You're into the 97th minute of a game, and we're sort of strung across the middle of the park.

"The boy (Watson) finds an enormous amount of space to counter and break on us.

"We didn't really want to make a decision on Anel because of the importance of substitutes in extra-time. We had that ability to bring one on.

"We would have had the ability to bring another one on, and I think that would have been a crucial point, but to lose it. To lose it in that manner really stings.

"Whether it's lack of experience or a bit of leadership where we just go we just see the game out but that wasn't to be and they find a fabulous winner."

It was yet another miserable day in the capital for the Blades, who have failed to win their last eight games at Wembley, with their last coming in the 1925 FA Cup final. 

They have also now failed to gain promotion in all five of their Football League play-off finals (four in the second tier, one in the third tier), the outright most play-off finals a single club has played without being promoted. 

But a defining moment in the contest came with the Blades 1-0 up, with Harrison Burrows believing he had doubled his team's advantage with a bouncing volley into the bottom corner. 

However, the goal was chalked out for an offside against Vinicius Souza, a decision confirmed by a pitchside review. 

Wilder believed that moment swung the momentum in the game, telling Sky Sports: "They've taken their opportunities. The goals are disappointing from our point of view. 

"The manner of the goals, the shape of the team from that point of view - we can do so much better.

"I never felt we were under major threat. I thought we started off the game ever so well. I know there is going to be a subjective decision regarding the VAR.

"One thing I will say - I don't think that having played 46 league games and two play-off games it all of sudden comes into play and I think their manager said that before the game but there we are, big moments.

"I think if we go 2-0 up we win the game comfortably, I think that really punctures them but I thought that gave them belief, that gave their supporters the belief and, from that moment the last sort of 10 minutes of the first half and maybe the first 10 minutes of the second half gave them some energy."