Bayern Munich sharpshooter Robert Lewandowski's 40th goal of the season helped see off Union Berlin as the Bundesliga leaders returned from the coronavirus suspension with a comfortable 2-0 victory.

Borussia Dortmund moved within a point of the perennial champions thanks to their thumping 4-0 win against rivals Schalke on Saturday, but Hansi Flick's men managed to restore their cushion in the capital.

Union were organised but lacked attacking spark in Sunday's clash, with Lewandowski's spot-kick and a Benjamin Pavard header enough to see Bayern triumph at the empty Stadion An der Alten Forsterei.

Flick's men were far from their best on their return from the coronavirus suspension, but they did their job diligently against well-drilled Union as they restored their four-point lead at the top.

Thomas Muller saw a first-half opener ruled out for offside, but the visitors would go into the break ahead after former Dortmund defender Neven Subotic caught Leon Goretzka in the box.

Lewandowski, who was able to recover from a knee issue during the league's suspension, coolly slotted home the resulting penalty five minutes before the interval to make it 40 goals in all competitions - the fifth straight season he has managed to reach that figure.

Union remained under the cosh for the remainder of the match but it took until the 80th minute for Bayern to notch a second, with Pavard rising to meet a Joshua Kimmich corner with a thumping header.

In the day's other game, Struggling Mainz fought back from two goals down to salvage a 2-2 draw at Cologne as football returned to the RheinEnergieStadion.

The hosts had got off to a flying start when Mark Uth fired them in front from the penalty spot in the sixth minute after a foul by Moussa Niakhate.

Mainz had a chance to equalise through Robin Quaison but Cologne doubled their lead early in the second half through a Florian Kainz header.

But the visitors pulled one back against the run of play just past the hour mark when Bote Baku crossed for Taiwu Awoniyi to convert his first Bundesliga goal.

Quaison missed a chance to equalise before Pierre Kunde Malong sealed a point with a superb solo effort, taking advantage of some dismal Cologne defending to dribble through the middle and fire the equaliser in the 72nd minute.