Bayern s Kingsley Coman, center, celebrates with Thomas Mueller, left, and Corentin Tolisso after scoring his side s fourth goal during the German Bundesliga soccer match between 1. FC Union Berlin and FC Bayern Munich in Berlin, Germany, Saturday, Oct. 30, 2021. AP
Three days after being thrashed 5-0 at Moenchengladbach in the second round of the cup, Bayern bounced back with two quick goals as Lewandowski converted an early penalty, then drilled home a free-kick.
"It's annoying that we conceded two goals, but we are happy to have shown a response," said Bayern captain Manuel Neuer.
The Bavarian giants ended Union's record of 21 league games unbeaten at home as Leroy Sane, Kingsley Coman and Thomas Mueller also grabbed goals, while Julian Ryerson and Niko Giesselmann scored for Union.
Lewandowski has now scored 12 goals in 10 Bundesliga games this season having scored a record 41 times in 2020/21.
A supposed leaked copy of the Ballon d'Or rankings, which has Lewandowski in first place with Lionel Messi second and Karim Benzema third, has been dismissed as fake by organisers France Football.
However, the Poland striker remains one of favourites with the winner to be announced on November 29.
Lewandowski fired Bayern ahead from the penalty spot following a Union handball, then curled in a free-kick to establish Bayern's domination.
Mueller tapped Coman's cross outside the reach of the Union goalkeeper Andreas Luthe for Sane to tap in at the far post.
Union's last league home defeat was back in September 2020 and the hosts fought to keep their record.
Japan midfielder Genki Haraguchi pinged a pass across the six-yard box where Giesselmann fired past Neuer to pull a goal back.
A Sheraldo Becker goal was ruled offside as it stayed 3-1 at half-time.
Union kept up the pressure, but Bayern scored against the run of play when Coman fired home from a tight angle.
The hosts refused to back down.
Substitute Kevin Behrens flew down the right wing and tucked his pass back inside for fellow replacement Ryerson to smash home, making it 4-2 on 65 minutes.
Mueller scored Bayern's fifth after a defence-splitting pass from Dayot Upamecano, making amends after a poor display at Gladbach on Wednesday.
Bayern's win could have come at a cost as Lucas Hernandez limped off with an ankle injury.
Dortmund, whose star striker Erling Braut Haaland remains sidelined by a hip injury, stay second and a point behind Bayern after their 2-0 win at home to Cologne.
Thorgan Hazard and Haaland's replacement Steffen Tigges scored the goals as Dortmund warmed up for Wednesday's Champions League match at home to Ajax.
Third-placed Freiburg, who play Bayern in Munich next weekend, remain the only unbeaten team in Germany's top flight this season with a 3-1 win at Greuther Fuerth.
Wolfsburg's new head coach Florian Kohfeldt made a winning start, ending the visitors' four-match losing streak with a 2-0 win at Bayer Leverkusen thanks to goals by Maximilian Arnold and Lukas Nmecha.
Wolfsburg finished with ten men after defender Maxence Lacroix was sent off for a second yellow card in the 96th minute while Leverkusen striker Lucas Alario had a penalty saved in stoppage time.
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