When Robert Lewandowski emerged for the warm-up at the Allianz Arena ahead of this eagerly awaited battle of European heavyweights, he was given a mixture of applause and boos from the home fans.

Bayern's second-highest all-time scorer, Lewandowski remains a divisive figure. He made outstanding contribution to Bayern's incredible success, but after eight trophy-laden years as the German giants' attacking lynchpin, the Polish talisman forced his way out of Germany in acrimonious fashion and joined Barcelona this summer.

The 34-year-old didn't have to wait long for the reunion with his former club as Barca got the chance to take on Bayern in the group stages of this season's Champions League on Tuesday night. 

Optimism seems to be in the air. There has been little adaptation needed for Lewandowski in Spain as he netted six times in five La Liga matches for his new team. He also opened his European account with a hat-trick in Barca's brilliant 5-1 win against Viktoria Plzen last week.

The Spanish powerhouse's infamous 8-2 defeat at the hands of Bayern in Lisbon in 2020 has been long forgotten.

"Barcelona have top players, play good football and 'Lewa' is up front, he uses every opportunity," observed Bayern sporting director Hasan Salihamidzic. "We have to shift up two gears, even three against them."

Salihamidzic's warning, however, fell on deaf ears. 

Right from the first minute, Barca stars showed more hunger and aggression in every tackle and pass while their Bayern counterparts were lethargic to say the least. Julian Nagelsmann's side struggled to repel wave after wave of Catalan attack with their goalkeeper and captain Manuel Neuer being the busiest player on the pitch before the break.

But the only blot in an otherwise positive first-half for Barca was none other than the wastefulness of their talisman Lewandowski. He uncharacteristically fired the best chance of the game over the crossbar and missed two more glorious scoring opportunities in a highly entertaining 45 minutes.

To his credit, Nagelsmann spotted Bayern's problem in dictating the tempo of the game and sent on Leon Goretzka to add more height and physicality to their midfield. His arrival duly turned the tables as Barca's intensity and ferocity on and off the ball had gradually evaporated.

Bayern's knockout punch came in quick succession. Lucas Hernandez headed in at the near post from a corner before Leroy Sane seal the win with a dazzling clipped finish. There's something special about seeing Bayern in such ruthless and efficient mode. It often takes them just a few minutes to kill the game even when they failed to hit top form.

"Barca had the better chances in the first half. We had to rely on Manuel [Neuer]," Nagelsmann said in his post-match press conference. "After the break we were more aggressive. We quickly scored two goals. We basically won because of higher efficiency."

The thrilling 2-0 triumph means Bayern have now won by a margin of 19 goals to Barca's four during their last five meetings. But Barcelona coach Xavi Hernandez remained defiant after their latest setback.

"We made six or seven big goal chances but missed them and Bayern took their opportunity," he said. "We competed, we played very well and had we scored it would have been a completely different match... This is the Champions League though, you need to compete and you try to avoid the marking error at the corner which let them go 1-0 up."

As for Lewandowski, this wasn't the homecoming he dreamed about. He was not on Bayern's side anymore, but it didn't matter. Bayern have managed to move on.