The Red Devils moved up to sixth on the English Premier League with the victory in the five-goal thriller against lowly Sheffield United, although they had to come from behind after Henderson’s mistake.
Henderson, who spent the last two seasons on loan at Sheffield United, got his opportunity with David de Gea on the bench, despite the Spaniard keeping a clean sheet against rivals City on the weekend.
The young goalkeeper dwelled on the ball for too long inside his own box, allowing Oliver Burke to tackle and dispossess him, before prodding to David McGoldrick to score a fifth minute opener.
Manchester United responded with a double from Marcus Rashford and another from Anthony Martial to claim the win, although McGoldrick pulled one back late before Henderson made a crucial save in stoppage time to deny Lys Mousset.
“Good, bad and the ugly, maybe in a different chronological order but it’s a test and a learning curve, Dean’s always learning,” Solskjaer said.
“He comes back here and he’s probably been looking forward to this for a long, long while and to get that start, it just shows his character in the rest of the game.
“When you’re a young keeper you’re going to make mistakes and he’s going to have to learn to redeem himself, which he did.
“He kept his composure, played really well after that. He knows next time that when Oliver Burke is going to close him down he cant dwell on the ball as he did.”
The result leaves the Blades rock bottom and six points adrift of 19th-placed West Bromwich, plus nine points away from escaping the drop zone.
Elsewhere, Aston Villa peppered Burnley’s goal with 27-6 shots but the sides couldn’t be split in a goalless draw. Burnley occupy 17th spot, just outside the drop zone having enjoyed a decent recent run, conceding only one goal in their past five games, excluding the heavy loss to Manchester City.