When Erik ten Hag predicted in the pre-game briefing that Manchester United could have another injury nightmare, the manager surely ­cannot have expected that to occur the next day, in the opening match of the team’s US tour. On 14 minutes in the game, though, he was forced to relive last season, when a total injury count of 66 was viewed as a prime factor in the club’s eighth‑place finish. At this juncture Rasmus Højlund, Ten Hag’s star No 9, was forced off. Twenty minutes later the Dane was followed by Leny Yoro, the new £52m centre-back. To this case of injury was added the insult of a late winner for ­Arsenal as Gabriel Martinelli darted across James Scanlon and beat André Onana with less than 10 minutes left. The Gunners probably deserved the 2-1 victory as they created more chances, though neither Mikel ­Arteta’s or Ten Hag’s teams were ­pictures of fluidity. After this came the pre-agreed penalty shootout which ended in a 4-3 win for United, Jadon Sancho the player with the decisive kick. Before this Højlund felt joy and despair. The clock showed 10 ­minutes played when he exposed the callow­ness of the 17-year-old Ayden Heaven, who allowed the striker to gather Marcus Rashford’s pass along the left, then backed off and off. Once inside Arsenal’s area, Højlund pulled the trigger, Karl Hein flapped at the ball, and in it rolled for a 1-0 lead. There, the joy. Next, after Aaron Wan-Bissaka raced along the right and crossed and Højlund nearly scored again, came the despair. Ben White had put him off with a challenge for this latter opening, but whether this caused the problem was unclear. Clearer was how, when Højlund went to ground, no chances were taken and the 21-year-old walked off to be replaced by ­Hannibal Mejbri, who took up the centre-forward role. Ten Hag was asked later about the striker, and the defender Yoro. “It’s too short, we have to wait over 24 hours then ­hopefully we will know more,” he said. “We were very careful ­especially with Leny. He did only 50% of the training sessions. That is very ­disappointing that he came off but let’s be positive and see what is coming out.” Before that, Yoro gave United an early scare when he missed the ball and Gabriel Jesus stole in. As at ­Murrayfield on Saturday against Rangers’ Cyriel Dessers, Yoro’s pace and 6ft 3in frame allowed him to recover and stick a long leg out, Onana gathering the ball. United’s No 1 was given ­little chance with Jesus’s equaliser, though. Ethan Nwaneri took Onana out of the equation when sliding the ball to the Brazilian who tapped in. If there was a firm hint of offside, no VAR meant it stood. Yoro could not carry on when he hit the turf with the problem that caused his removal. Unlike Højlund, the French defender moved gingerly as he headed to join his teammate in the changing room. This meant Rhys Bennett, a 20-year-old with a single League Two appearance on loan for Stockport County, entered. These two pieces of ill fortune took Ten Hag’s XI down to seven frontline players to Arsenal’s eight, led by the captain, Martin Ødegaard. Mason Mount was perhaps United’s ­standout performer, as he showed quick thought and feet, operating as a No 10, finding the time and space to mark a better class of footballer. At the break Arteta made two changes – Heaven and Nwaneri for Salah-Eddine Oulad M’hand and Jakub Kiwior – and Ten Hag made 10 substitutions, as only Onana remained. United’s keeper staying on proved prudent because when Leandro Trossard cut into the area and unloaded a shot at close range, Onana’s cat-like reflexes had him beating the ball out. Arsenal were flipping ­possession about where they liked. In the final third, their movement was ­causing their ­opponents to scurry about ball‑chasing. So, when United broke, Sancho’s mazy run along the right that drew Arsenal back was welcome. As was his calm pivot and pass to Maximillian Oyedele. United’s pre-season form had been a 1-0 defeat by Rosenberg and a 2-0 win against Rangers. For this outing, Omar Berrada watched on. The chief executive was joined at the 70,240-capacity SoFi Stadium by his sporting director, Dan Ashworth, the technical director, Jason Wilcox, and Dave Brailsford, who oversees for Jim Ratcliffe, plus another of the co-owners, Avram Glazer. Arsenal had drawn 1-1 with Bournemouth on Thursday, Fábio Vieira their scorer, and the Portuguese midfielder was brought on among a raft of changes by Arteta just after the hour. Another substitute, Kai Havertz, had the ball taken off his head by Christian Eriksen when the German looked set to score. Next came Martinelli’s decisive intervention.