Watch the Bundesliga LIVE on beIN SPORTS | Sign up to take advantage of our 7-day free trial | AU | NZ

Granit Xhaka’s brilliant 20-yard strike gave Leverkusen the lead after just three minutes, but a well-worked headed equaliser from Dominik Kohr came close behind to give the relegation struggler hope.

Xabi Alonso’s side was spared any further anxiety when Robert Andrich tried his luck from range in the 68th minute and Zentner allowed a gentle effort to squirm through his gloves and over the line.

The relief around the ground was as tangible as the keeper’s despair and, when Jessic Ngankam was sent off late on, the points were secured.

In doing so, Leverkusen stretched its unbeaten run to 33 games in all competitions, a new German record at the expense of rival Bayern Munich.

The hosts wasted no time stamping their authority on proceedings, Jonas Hofmann winning a free-kick in opposition territory.

Xhaka acted as first receiver before sliding in Alex Grimaldo down the left flank. His cross was deflected back to the Swiss midfielder, who proceeded to swing his weaker left foot and send a curling, dipping first-time effort sailing over a wrong-footed Zentner.

Xhaka marked his first goal since joining the club from Arsenal last summer by feeling for his hamstring.

Alonso briefly looked concerned on the touchline, but as his team-mates joined in it quickly became clear it was an in-joke rather than a genuine fitness setback.

But Mainz was the one celebrating five minutes later, Nadiem Amiri’s deft chip over the top creating the opening against his parent club.

Silvan Widmar was onside by a whisker as he met the ball with his head and squared it back across the penalty box and, although the ball did not land perfectly for Kohr, he timed his diving header wonderfully well to power the ball home from 10 yards.

Xhaka, Hofman and Grimaldo all had sights of goal as the home side pushed to reclaim the advantage, but Mainz stood its ground.

Mainz came desperately close to going ahead after 50 minutes, Leandro Barreiro stretching to meet Amiri’s free-kick at the far post, only for Jonathan Tah to mop up calmly when he could easily have scored an own goal.

There was another warning when Edmond Tapsoba’s poor pass offered Lee Jae-sung a free strike, only for the Korean to miss the target completely.

Things were beginning to get scrappy amid a flurry of bookings, when Andrich’s pot shot changed the game. The ball swirled slightly on its way to Zentner, but there was no hiding his culpability as he waved it tamely into the side of his net.

Ngankam saw red with 10 minutes left on the clock, a dangerous slide on Xhaka upgraded from a caution after a review, allowing the league leader to see out its evening safely.