Kane's late pen helped his team avoid a first defeat of the season and also marked his 50th goal for Bayern in 2025, the first time the former Tottenham striker has ever hit that mark for his club in a single calendar year.
Robert Lewandowski, Kane's predecessor in the front line at Bayern, also accomplished the feat in 2021 when he scored 58 times for the club that year.
Heavy underdogs Mainz were playing their first league game under new coach Urs Fischer, who formerly enjoyed great success with Union Berlin. Fischer was appointed last week to replace Bo Henriksen after Mainz's dismal start to the Bundesliga.
Bayern dominated from the start and Lennart Karl -- the team's newest star -- opened the scoring in the 29th when he was well placed for a tap-in to Serge Gnabry's cross.
It was Bayern's 50th Bundesliga goal of the season, a record after just 14 rounds of the league.
But the home team failed to make more of its superiority and was shocked before the break when defender Kacper Potulski equalized with a header after William Böving's free kick. It was the 18-year-old Poland youth international's first Bundesliga goal in just his second league appearance.
The visiting fans were in dreamland when Lee Jae-Sung scored with a header to Stefan Bell's deep cross in the 67th, but there was still plenty of time for Bayern to respond.
Vincent Kompany sent on Senegal forward Nicolas Jackson for his last appearance before going to Morocco for the Africa Cup of Nations starting Dec. 21. Canada's Alphonso Davies had already gone on for his first league appearance in nine months after recovering from a serious knee injury.
Potulski was penalized for holding Kane and the England forward dusted himself off for what was his 17th Bundesliga goal of the season.
Information from The Associated Press was used in this story.
