But for ex-Chelsea star Pat Nevin, Smalling was not to blame for the mistake.
Manchester United had led at Molineux thanks to Scott McTominay’s early strike.
A Diogo Jota strike levelled things up for Wolves before half time.
And the hosts stunned Ole Gunnar Solskjaer’s men when Smalling converted into his own net moments after Ashley Young had been sent off.
Both Smalling and his defensive partner Phil Jones failed to deal with a routine ball into the box that led to Wolves’ winner.
Yet it was David De Gea who Nevin reckons deserves the blame for the blunder.
The Spaniard remained rooted to the spot as the ball went past him, before Smalling clattered into the keeper.
“A scrambled goal. The goalkeeper has to take everything,” Nevin said on BBC 5 Live.
“He has not had much to do.”
Indeed, Wolves managed just two shots on target all game as they stunned top-four chasing United.
Nevin was impressed with goalscorer but was critical of Paul Pogba after the game.
“Scott McTominay was far better than Paul Pogba on the day,” Nevin added.
“Wolves are a very good side, specifically a good passing side.
“If you give them space in midfield they will control games.”
As for Solskjaer, he was all praise for McTominay but bemoaned United’s inability to shut out their hosts.
“I think we played some fantastic stuff, first 20 minutes we should have been two or three up and I’m not exaggerating,” he said.
“We didn’t pounce on big moments in the game.
“Scott McTominay played really well tonight, he’s been excellent. He gave us a goal threat, energy and legs – very pleased with him.
“There’s a couple of mistakes from us. We gave them that first goal, we have to be honest.”