Hoffenheim missed out on an opportunity to move into the Bundesliga's top four, suffering a heavy 5-1 home defeat by a Mainz side playing under newly appointed coach Achim Beierlorzer.
The hosts failed to win for the first time in five games as the visitors moved out of the relegation zone to 13th spot with only their third victory of the campaign.
Beierlorzer, who was sacked by struggling Cologne nine days before taking over at the Opel Arena on November 18, started his reign successfully despite Ridle Baku's first-half red card as Cameroon midfielder Pierre Kunde Malong scored twice to open his account for the season.
Levin Oeztunali claimed the first goal of proceedings on 33 minutes before his midfield partner Baku was dismissed seconds before the break for a studs-up challenge on the home side's Sebastian Rudy.
Mainz continued to attack in the second half, peppering the Hoffenheim box until an own goal from Pavel Kaderabek in the 52nd minute doubled their lead.
Kunde tapped in for his first of the season 10 minutes later before Andrej Kramaric claimed a consolation effort for the home side in the 83rd minute.
Jean-Paul Boetius snuffed out any chance of a comeback in the 90th minute, however, scoring on the break to make it 4-1 and Kunde added his second two minutes later to complete the rout.
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