Alexander Zverev suffered a surprise Hamburg Open second-round exit at the hands of Alexandre Muller, who claimed the biggest win of his career.

The home favourite's hopes of reaching a third successive final at the tournament were ended, as he fell 6-3 4-6 7-6 (7-5) after two hours and 40 minutes.

Zverev, champion in 2023 and runner-up last year, was broken in the fourth game of the opening set and was unable to hit back.

The top seed did break at the first attempt in the second set, though Muller replied in game five to leave it in the balance.

Zverev was in danger of a straight-sets defeat at 40-0 down in game nine, but he rescued three break points to eventually hold, before breaking to 15 to force a decider.

Both players exchanged breaks inside the opening four games as the final set ultimately went to a tie-break.

Zverev appeared in control at 5-3 up, only for Muller to reel off the last four points and seal his first career top-five victory.

Elsewhere, 2020 champion Andrey Rublev advanced to the quarter-finals after a 6-3 7-5 victory over Justin Engel, and is the only former winner remaining in the draw.

Meanwhile, Jiri Lehecka was also a straight-sets winner against fourth seed Francisco Cerundolo.

BIGGEST WIN OF HIS CAREER@Alex2Mumu stuns the top seed Zverev to claim his first Top 5 scalp! @hamburgopenatp | #bitpandahamburgopen pic.twitter.com/FLFt2imeDU

— ATP Tour (@atptour) May 21, 2025

Data Debrief: Muller stuns Zverev to seal personal bests

Zverev was seeking a fourth quarter-final in as many appearances at the Hamburg Open. 

Not since 2016 had he failed to progress beyond the last eight in this event, though his cause was not aided by 47 unforced errors against Muller.

The German subsequently suffered only his third defeat in 21 matches against French opponents.

Muller, who was 0-5 against top-five opponents prior to Wednesday, broke new ground to set up a quarter-final clash with either Felix Auger-Aliassime or Giovanni Mpetshi Perricard.

The Frenchman also achieved a personal best by registering a career-high 17th match win in a single ATP season.