Bayern top-scorer Jamal Musiala, who turned 20 on Sunday, swept in Thomas Muller's pass to complete the scoring.

Bayern are above Borussia Dortmund on goal difference while Union stay third.

Union began the match level on points with Bayern and unbeaten in any competition since 13 November but did not have a shot on target as the hosts recovered from their 3-2 defeat at Borussia Monchengladbach.

In his first appearance since sustaining the injury on 8 November,Mane almost contributed to a more emphatic scoreline shortly after coming on.

The summer signing from Liverpool dribbled into the Union penalty area and set up Muller, whose effort was saved by visiting goalkeeper Frederik Ronnow.

Alphonso Davies was also twice denied by Ronnow as Bayern extended their unbeaten run at the Allianz Arena to 18 matches.

Dortmund briefly returned to the Bundesliga summit by winning 1-0 at Hoffenheim on Saturday in a seventh successive league win for Chelsea's Champions League opponents.

RB Leipzig are four points behind Bayern following their 2-1 victory over Eintracht Frankfurt. They overtook Freiburg, who drew 1-1 at home to Bayer Leverkusen, by a point.

The leaders next play when they visit relegation-threatened Stuttgart on Saturday, four days before they defend a 1-0 lead at home to Paris St-Germain in the second leg of the Champions League round of 16.