Champions Bayern Munich won 2-1 at Cologne on Saturday with goals from Thomas Mueller and Serge Gnabry returning them to the Bundesliga summit as coach Hansi Flick rested top scorer Robert Lewandowski. The Bavarians, who are in action against Salzburg in the Champions League on Tuesday and also face Borussia Dortmund in the Bundesliga next week, are on 15 points, ahead of Dortmund on goal difference. RB Leipzig are stuck on 13 points after suffering their first league loss of the season, a 1-0 defeat at Borussia Moenchengladbach. Lewandowski's absence was hardly felt with the visitors in control from the start despite Flick's rotation that also saw Leon Goretzka and Kingsley Coman rested. They earned a 13th-minute penalty when Gnabry headed the ball onto Marius Wolf's arm. In Lewandowski's absence Mueller stepped up to score his fourth goal of the season with a well-placed spot kick as he equalled former keeper Oliver Kahn's club record for most victories (260). Gnabry then got onto the scoresheet himself with a strong run down the wing and a powerful left-footed effort in first-half stoppage time to seal their fourth straight league win. "We did not have the feeling that we were very solid," Gnabry said. "We lost possession far too often in the second half. It was not our best game today but at the end we have the three points and we are happy." Cologne hardly ventured forward after the break and Bayern eased off, with second-half substitutions taking the pace out of the game. The hosts did score with Dominick Drexler's deflection to cut the deficit in the 82nd minute but couldn't challenge for an equaliser.