(CNN) -- Bayern Munich's hopes of taking a record lead into the Bundesliga's winter break were dented by a 1-1 draw at home to Borussia Monchengladbach on Friday.
The result left Jupp Heynckes' team 12 points clear at the top after 17 rounds, but second-placed Bayer Leverkusen can reduce that to nine by winning at home to Hamburg on Saturday.
Borussia Dortmund set the record of a 10-point halfway lead in 2010, but the third-placed defending champions can only close the gap to 11 by winning at Hoffenheim on Sunday.
Bayern, who won a record opening eight matches of this season, had hoped to put on a show to match the planned post-game "thank you" party for the 71,000 fans at the Allianz Arena, but Gladbach killed the mood by taking the lead in the 21st minute.
Thorben Marx fired home from the penalty spot after Bayern defender Jerome Boateng handled a cross by Tolgar Cigerci in the visitors' first real attack of the match.
"I don't know how the referee could class that as a penalty," Boateng told reporters.
"I seriously don't think it was justified. I think we deserved to win."
Bayern lost $52 million August signing Javi Martinez to injury before halftime, but it was the Spanish midfielder's replacement Xherdan Shaqiri who netted the equalizer.
Heynckes -- who was born in Monchengladbach and also played for and managed the club -- also brought on last season's top scorer Mario Gomez for his early-season replacement Mario Mandzukic just 11 minutes after the break.
Germany striker Gomez, who missed three months with injury, helped make space for Shaqiri -- who took advantage of a slip by Marx to fire in a left-foot shot at the near post just before an hour's play.
It was the 21-year-old Switzerland international's first Bundesliga goal since signing from Basel in preseason, though he had netted in the Champions League earlier this month and in the German Cup in August.
Gladbach held on to move up to sixth place as Bayern dropped points for just the fourth time this season, having lost only once.
Bayern will begin the four-week winter break following Tuesday's German Cup last-16 trip to Bundesliga strugglers Augsburg on Tuesday.
The match may be a further test for Mandzukic, who scored nine league goals before Gomez returned from ankle surgery in mid-November -- but none since.
Gomez, who matched the Croatia forward's three goals at Euro 2012, has netted three times in seven appearances since his return.