Manchester United collapsed to a 4-2 defeat as Ruben Amorim’s AC Milan came from behind to win in Poland.
Harry Maguire had opened the scoring in the second minute when he headed in from Bruno Fernandes' corner and when Amad Diallo came close to a second soon after it looked likely to be a difficult day for Amorim in his first meeting against his former club.
But after Senne Lammens did well to keep out Ruben Loftus-Cheek, Goncalo Ramos laid an equaliser on for Samuel Chukwueze. United then squandered the opportunity to go in ahead at the interval when Fernandes had his firmly struck penalty well saved.
Patrick Dorgu did seized on a sloppy back-pass by Filippo Terracciano to restore United's advantage but they were pegged back once more when Alphadjo Cisse ghosted in at the far post as Chukwueze tore Michael Carrick's team apart on the right for the Rossoneri.
The winger set up Ramos to nod Milan in front for the first time and it was that same flank that was exposed when Ruben Loftus-Cheek made it four. With the Premier League season under way next weekend it was a little alarming how things unravelled.
The introduction of the United substitutes did not help with Lisandro Martinez easing his way back after his World Cup exertions and Kobbie Mainoo also returning. Marcus Rashford came on too for his first appearance for his boyhood club in 20 months.
2 - GOAL! Maguire heads in Fernandes' corner
6 - CLOSE! Amad robs Pavlovic and is almost in
15 - SAVE! Lammens does well to deny Loftus-Cheek
37 - GOAL! Ramos sets up Chukwueze for a tap-in
41 - PENALTY SAVED! Fernandes denied from the spot
51 - GOAL! Dorgu seizes on poor pass to score
57 - GOAL! Cisse ghosts in at the far post to level
61 - SUB! Rashford on for first United game in 20 months
68 - GOAL! Ramos nods in from Chukwueze's centre
71 - GOAL! Loftus-Cheek nets after racing down the right
Man Utd head coach Michael Carrick:
"We're disappointed with it. We didn't play well today. There are reasons for that and we need to improve. Some of the boys were playing their first minutes. Different reasons - but no excuses. We didn't play very well.
"Overall, we are ready for next week. A lot of the boys will be better off for the minutes. We've done a lot of work on the training pitch, the performances in the games have been pretty good. We're still in good spirits going into next week.
"We've got a good squad. There are decisions to be made. We've got another week's training to get ready for next week. There's a whole different feeling when it's the first league game of the season. We will be there."
There have been positives for Manchester United in pre-season with Andrey Santos emerging as a real asset for the club and while Youri Tielemans is still settling in, the new-look midfield has promise. But this defeat showed that others are far from ready.
Perhaps that is to be expected with the likes of Martinez, Mainoo and Rashford working their way towards fitness but the first Premier League game of the season away to Hull is less than a week away now and it is not the sort of game in which United can slip up.
The system is settled and Carrick is working on those patterns but question marks over the personnel remain. Can Luke Shaw really be relied upon as heavily as he was last season? Do United still need another midfielder? More questions than answers in Poland.
July 18: - Helsinki
July 24: - Trondheim
August 1: - Stockholm
August 8: - Gothenburg
August 12: - Dublin
August 15: - Wroclaw
