Bayern were looking for a 17th straight win of the season
Bayern Munich's record run of wins since the start of the season is over despite a late Harry Kane equaliser against Union Berlin.
Their 16 victories in 16 games in all competitions before Saturday's Bundesliga clash was the best ever start to a season by any men's team from the top five European leagues.
But they missed the chance to equal a club record of victories at the start of a Bundesliga season thanks to this late draw.
Bayern fell behind when Danilho Doekhi's effort following a corner slipped under keeper Manuel Neuer.
This was the first time they had trailed in a match or conceded a goal in the first half this season.
However, Union's lead was soon wiped out by Diaz's third goal in two games - and it was a stunning effort.
Josip Stanisic's slide rule pass looked to be going out but in three touches Diaz kept the ball in play on the byeline, nudged it past the defender on the spin and launched a stinging effort in at the near post from the tightest of angles.
Kane's unusually quiet afternoon was summed up when he inadvertently headed a Union free-kick straight into the path of Doekhi who finished past Neuer.
But the England captain made amends in the 93rd minute when he headed in from Tom Bischof's cross for his 13th Bundesliga goal of the season.
Bayern will return from the international break with a home match against Freiburg on Saturday, 22 November (14:30 GMT), while Union will travel to Hamburg to play St Pauli on Sunday, 23 November (16:30).
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