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The 20-year-old triumphed 6-3 3-6 7-6 (7-1) in a three-and-a-half-hour marathon, saving a remarkable 21 of 22 break points, including five in the final set, to follow up his 2023 triumph in Lyon.

Fils raced into a 3-0 lead in the opener before having to fend off four break points in the fifth game as he took the lead, but defending champion Zverev roared back in the second set.

Zverev got the breakthrough six games into a back-and-forth second as the big-serving German forced a decider.

Having saved break points at 4-4 and 5-5 in the third, Fils came on strong in the tie-break, recording the biggest win of his career and his fourth versus a top-10 opponent.

Fils is just the second player younger than 21 to triumph at the Hamburg Open, after Roger Federer in 2002 and Lorenzo Musetti in 2022.

Zverev, meanwhile, missed the chance to become the fifth man to defend the Hamburg title in the Open Era, after Eddie Dibbs (1973-1974), Andre Medvedev (1994-1995), Federer (2004-2005) and Nikoloz Basilashvili (2018-2019).