Raphael Guerreiro scored the only goal as Bayern Munich beat Union Berlin 1-0 at home on Wednesday, with the visiting coach sent to the stands for grabbing Leroy Sane's face.

With Bayern in front after Guerreiro's second-half strike, Union striker Kevin Behrens was brought to the ground in the penalty box by a home defender with 20 minutes remaining.

The Union players and staff became increasingly incensed as VAR seemingly decided not to intervene, with visiting manager Nenad Bjelica grabbing Sane's face and pushing the winger as he tried to take a throw in minutes later.

Bjelica saw straight red and was sent to the stands, arguing with home fans as he was escorted by stewards, while Sane received a yellow card for retaliating.

Bayern held on as Union sought a late equaliser, but the tension among the home side was clear, with the German champions sitting in the unfamiliar second spot, four points behind Bayer Leverkusen.

The win may however be costly for the home side, who lost Dayot Upamecano to a hamstring injury, bringing former Spurs defender Eric Dier onto the pitch for the first time in Bayern colours.

With Kim Min-jae on Asia Cup duty, Matthijs de Ligt could be Bayern's only fit centre-back should Upamecano fail to return in Saturday's clash with Augsburg.

Bayern had lost 1-0 at home to Werder Bremen on Sunday, failing to score a goal for the first time in four years.

Bayern last lost two league matches at home in 2001, highlighting the historical dominance of Germany's most successful club.

Union, having hit the heights of Champions League qualification last campaign, travelled to Munich stuck in the middle of a relegation battle, sitting one place and three points clear of the drop in Wednesday's rescheduled fixture.

Having said on Tuesday his side were "well below expectations" in Sunday's loss to Bremen, Bayern manager Thomas Tuchel's half-time speech did the trick, Guerreiro scoring just a minute after the break.

Harry Kane hit the woodwork but the ball fell at the feet of the Portuguese, who booted in the opener.

Kane looked to have scored his 23rd goal in just his 18th league match shortly after Guerreiro's opener, but VAR found Sane offside in the build-up.

Bayern's goal forced Union to push forward and Behrens hit the turf under heavy attention from the home defence on the counter, leading to Bjelica's clash with Sane.

The tension continued in the dying stages, the referee handed out four yellow cards in injury time, including for England captain Kane.