Arthur Fils has denied world number four Alexander Zverev back-to-back titles at the Hamburg European Open in a testy three-and-a-half-hour thriller.

Fils edged a close encounter 6-3, 3-6, 7-6(7/1) to win his second tour-level title and first ATP 500 crown, saving 21 of 22 break points faced en route to the crown.

The biggest of them included an underarm serve at 5-5 and 30-40 in the deciding set.

It caught German Zverev off guard and, while it was called wide after umpire Timo Janzen checked the mark, Fils won the point with a kicking second serve that Zverev could not get back into play.

The Hamburg crowd booed and jeered at Fils, who pointed to his ear, shrugging, shaking his head and firing them up further.

Shortly after that, Fils confronted Zverev at the change of ends and had to be pulled away by the umpire as the crowd's boos restarted.

Zverev did not take the loss to the 20-year-old Frenchman well, barely making eye contact in a frosty handshake at the net, before shaking his head, muttering something to himself and arguing with the umpire.

"I think that I did everything to win this match," Fils said on the court after the match.

"I got cramps at 5-5 in the third. I'm cramping, trying underarm serves because I cannot serve.

The mood seemed to have calmed somewhat by the trophy presentation, when Zverev sprayed Fils with champagne and both had smiles on their faces.

The win sees Fils, who is expected to rise inside the top 20 for the first time, improve to 1-2 in his all-time head-to-head record against Zverev, having lost to the 2023 champion in last year's semifinal and in the quarters on grass at Halle last month.

It is Zverev's third final in this claycourt season, leading into the Paris Olympics at Roland Garros, with the German claiming the Rome title but missing out at the French Open.

Fils, meanwhile, claimed his second title of the year, adding to his crown in Bordeaux in May.

He will be one of the brightest local hopes at the Paris Games.