Both teams came racing out of the blocks at BayArena, but it was Leverkusen who struck the first blow inside three minutes as Granit Xhaka produced a shot and a celebration to remember.
After curling spectacularly over the helpless Zentner and opening his Bundesliga account for the campaign, Xhaka pretended to pull a hamstring before belatedly breaking into a pre-rehearsed routine with teammates, as manager Alonso’s visible angst immediately turned to relief on the touchline.
Mainz were in no mood to let the hosts slip into cruise control, however, after newly-appointed boss Bo Henriksen restored belief in the squad by winning on his dugout debut last time out.
The Dane’s impact was clear to see as Leverkusen were frustrated for much of the first period, and their lead didn’t last long, with Dominik Kohr contorting his body to head Karnevalsverein level in a frantic opening to the contest.
Mainz had more opportunities to put the cat amongst the pigeons in the second half, but their lack of potency up top has been a sticking point all season, and neither Phillipp Mwene nor Lee Jae-Sung managed to find the target when given clear sights of goal.
The visitors were then punished in cruel fashion, as Robert Andrich’s swerving shot from distance flummoxed Zentner and somehow found its way into the net, edging Leverkusen a step closer to their first-ever Bundesliga crown.
Substitute Jessic Ngankam was sent off for a reckless tackle late on as relegation-threatened Mainz went down to 10, and ultimately failed in their quest to notch a first away Bundesliga win since last April.
As for Leverkusen, victory gives them breathing room in the title race, but out-of-form Bayern Munich can cut the deficit to eight points with a win over RB Leipzig on Saturday.
Flashscore Man of the Match: Jeremie Frimpong (Bayer Leverkusen)
