London - Pep Guardiola was left struggling to explain Bayern Munich's 2-0 defeat by Arsenal in the Champions League on Tuesday, a result that ended his side's impeccable start to the season.
The Germans controlled huge swathes of the Group F game at the Emirates, had 68 percent of the ball, carved out several great chances but unusually lacked a killer instinct in front of goal.
Until Tuesday, Bayern had won the 12 games they had played in all competitions, setting a Bundesliga record of nine straight victories from the start of the season.
For once, goal-machine Robert Lewandowski could not find the net with Arsenal keeper Petr Cech and his inspired defenders thwarting the lethal Pole.
"We had enough chances to win the match, or at least not to lose, but congratulations to Arsenal for the win and we will meet again in two weeks in Munich," said coach Guardiola who has guided Bayern into the semi-finals in both seasons since taking over.
Pushed by reporters on what had gone wrong, the former Barcelona boss was stumped for an answer.
"I've got no explanation," he said.
"It's a mystery.
"In the second half we played well until the goal. In the end we played with a back three, we attacked everywhere, we had chances in the box, we had control, but in the end they scored two goals and we, none.
"But I'm proud tonight of the team. I like to win but we played well with a lot of courage. In the second half we played amazing. Maybe we didn't have too many chances but they didn't cross the halfway line."
Arsenal's opener in the 77th minute, coming just after Lewandowski was denied by a brilliant block by Laurent Koscielny, arrived following a rare error by Bayern keeper Manuel Neuer.
He came out to meet a Santi Cazorla free kick but flapped at the ball and substitute Olivier Giroud bundled the ball in.
Guardiola refused to blame Neuer who made a spectacular stop from Theo Walcott's point-blank header in the first half.
"He made some great saves," said the coach.
"Never in my life have I criticised a player for taking decisions whether they are correct or not. He took a decision in that situation and that's it."
Bayern and Olympiakos Piraeus have six points from three games in Group F while Arsenal and Dinamo Zagreb are on three.