Eric Maxim Choupo-Moting headed Bayern into an early lead before Lewandowski, the league's top scorer, struck twice to increase his league tally for the season to 28 goals.
Gnabry came off the bench to claim two late goals at the Allianz Arena on his first appearance since tearing his thigh a fortnight ago in Bayern's Club World Cup final win in Qatar.
The result sees Bayern bounce back in the Bundesliga after taking just a point from their previous two league games.
However, second-placed RB Leipzig can trim Bayern's lead when they host Borussia Moenchengladbach later on Saturday.
February 27, 2021