Munich: Mathys Tel's stoppage-time goal proved enough for Bayern Munich to beat Manchester United 4-3 in their Champions League opening game.
Tel scored with a spectacular finish in the second minute of injury time on Wednesday, restoring Bayern's two-goal lead just when United threatened to pull off another remarkable comeback after Casemiro scored in the 88th.
Casemiro did score again in the fifth minute of stoppages with a header to Bruno Fernandes' free-kick, but this time there was no fairy-tale ending for United, which beat Bayern with two late goals to win the 1999 Champions League final.
United had forced the initiative early as the old rivals met again in the group stage, but Harry Kane's penalty in the 53rd for 3-1 seemed to be the final blow for an injury-hit team low on confidence after starting the Premier League with three defeats in five games.
United was without the injured Luke Shaw, Harry Maguire, Tyrell Malacia, Mason Mount and Aaron Wan-Bissaka, and coach Erik ten Hag was forced to name three goalkeepers among his substitutes.
Ten Hag's counterpart Thomas Tuchel was suspended for his sending off in Bayern's quarterfinal loss to Manchester City last season. Assistants Zsolt Lw and Anthony Barry took charge.
United almost grabbed a shock early lead with Alphonso Davies sliding in to deny Facundo Pellistri from close range. Bayern goalkeeper Sven Ulreich denied Christian Eriksen from the rebound.
Bayern had to wait till the 20th minute for its first chance and had fortune on its side with United 'keeper Andr Onana deflecting Leroy San's harmless-looking shot inside the right post in the 28th after San had played a one-two with Kane.
"We started the game well and mistakes is part of football," United defender Victor Lindelf said.
"We tried to get back into the game, but we were playing against a very strong team as well. But of course, it's not the result that we wanted."
Serge Gnabry capitalized on San's blow by adding another goal four minutes later, sweeping a shot from distance inside the far post after a fine run from Jamal Musiala to set him up.
Hjlund scored with a deflected shot early in the second half, but Danish compatriot Eriksen was penalised through VAR for hand ball after Dayot Upamecano headed the ball into his hand. Kane duly converted the penalty for his first Champions League goal in a Bayern jersey. The six-time champion maintained control until Casemiro restored some excitement to the finish.
"It's a bit paradoxical. We were much better in the second half than we were in the first, and we lost the second in the end while we won the first, 2-0," Tuchel told broadcaster DAZN.
"It's very important for confidence and development. But there are still things that we have to do better."
Galatasary drew with Copenhagen 2-2 in the other Group A match.
Arsenal made a stylish return to the Champions League by sweeping aside PSV Eindhoven 4-0 at Emirates Stadium after a six-year absence from the competition.
Arsenal seemed determined to make up for lost time and jumped out to a 3-0 lead by the 38th minute on Wednesday with PSV goalkeeper Walter Benitez having made a couple of good saves by then to prevent an even bigger scoreline.
In a game played in driving rain throughout, Bukayo Saka, Leandro Trossard and Gabriel Jesus all scored in the first half, before Martin Odegaard added the fourth with a long-range strike in the 70th.
In the other Group B game, Sevilla drew 1-1 with Lens in Spain.