Kazakhstan's Astana fought back to beat a youthful Manchester United side 2-1 at home on Thursday, earning their first points in the Europa League's Group L this season.
United captain Jesse Lingard fired them ahead in the 10th minute with a fizzing low shot from 20 metres before Dmitri Shomko and a Di'Shon Bernard own goal turned the match on its head shortly after half-time.
United, who had already booked their place in the last-32, stayed top on 10 points from five games, but second-placed AZ Alkmaar, who have eight from four, can leapfrog them if they beat Partizan Belgrade at home later on Thursday.
Third-placed Partizan have four points and Astana three.
United manager Ole Gunnar Solskjaer, who left the bulk of his first-team players at home ahead of a busy Premier League schedule, was upbeat despite the defeat.
"You've got to put [the youngsters] on the pitch before you know if they're good enough," the club's former striker told Manchester United television.
"At times we were excellent and the short spells we let them push us back cost us in the end because it was a big 10-minute spell they had in the second half.
"These boys have learnt a lot and have given me food for thought and I'm very pleased with many of them. I'm just sorry they couldn't go away with a win because I think they deserved it."
United's team was packed with academy products, including three starters playing at senior level for the first time, and they took the game to Astana as Lingard delighted the 1,000 away fans with a scorcher into the bottom-left corner of the net.
Tahith Chong was guilty of an astonishing miss in the 54th minute when he fired over a gaping goal from five metres and United were punished shortly afterwards as Astana scored two quickfire goals.
Chong looked to have apologised for his misfire afterward but Solskjaer was in no mood to fault him after the match.
"Yeah, of course but he said the same in the dressing room, it's a difficult game if he scores and takes the responsibility but no forward or striker should worry about missing chances, that's about growing up, I think I did as well," he said.
Shomko equalised barely 30 seconds later when he steered a low shot from 10 metres past United's 36-year-old goalkeeper Lee Grant, who also made his full debut for the club.
Roared on by their fervent fans, the home side completed the comeback in the 62nd minute when Bernard diverted an Antonio Rukavina cross from the right into his own net.
Astana keeper Nenad Eric kept them ahead with a pair of acrobatic saves in the 78th minute, tipping over an Angel Gomes free kick before he denied Mason Greenwood from close range.
United will complete their group stage campaign at home to Alkmaar while Astana visit Partizan on Dec 12.