Arsenal, who won all eight of their games in the league phase, fell behind to a simple Leverkusen corner when Robert Andrich headed in moments after half-time.

But in the dying stages, substitute Havertz stepped up to convert against his former side after Noni Madueke was brought down in the box.

The Premier League leaders lacked fluency and the set-piece specialists were ineffective despite several dangerous free-kicks, but now need just to win at home next week to reach the quarter-finals for a third consecutive season.

With a young side still gelling after a summer rebuild, Leverkusen have been inconsistent this campaign but showed enough to suggest they could still threaten Arsenal at the Emirates next week.

Both sides were tentative in the first half, with Leverkusen wary of Arsenal's firepower and the Gunners even more risk averse than usual with next week's return leg at home.

Arsenal had two free-kicks near the hosts' box inside the opening four minutes, but both came to nothing.

Leverkusen were dangerous on the break, particularly through teenage forward Christian Kofane. The best chance of the opening period fell to Gabriel Martinelli, who blasted against the crossbar with 19 minutes gone.

Leverkusen turned up the heat after half-time and were ahead within a minute.

Martin Terrier forced an excellent fingertip save from David Raya from a Grimaldo cross after Leverkusen attacked straight from kick-off.

Grimaldo took the ensuing corner and found Andrich in acres of space at the far post, giving the Germany midfielder a simple header to score.

After the goal, Leverkusen manager Kasper Hjulmand -- who questioned the legality of the visitors' dead-ball tactics pre-match -- got involved in a fiery exchange with Arsenal's set-piece coach Nicolas Jover.

Arsenal's first corner came on the hour mark and was greeted with a huge cheer from the 2,100-strong travelling contingent.

Arsenal grew increasingly frustrated but were handed a lifeline when substitute Malik Tillman was adjudged to have fouled Madueke in the box.

Havertz, who was greeted with warm applause when subbed on, nervelessly slotted the ball into the bottom corner and reacted with a muted celebration against his first professional club.