An umpire was forced to step in and separate Alexander Zverev and Arthur Fils as tensions boiled over during the Hamburg Open final. Fils edged a third-set tiebreak to win his first ATP 500 title in a marathon contest which lasted three hours and 31 minutes.

Tempers flared during the final set of the match, with Fils launching into a verbal tirade at Zverev during a break in play. It came after the Frenchman tried an underarm serve which was initially called in, but was deemed to have been out upon further review.

The crowd did not approve of Fils' tactics and began to cheer his missed serves, while Zverev also seemed to take issue with the underarm serving. The two players later erupted into a blistering row, with Filers walking over to Zverev, who was sat in his courtside chair. The umpire stepped in to calm things down and put his hands on Fils to push him back to his side of the net.

A third-set tiebreak was eventually required to find a winner, with Fils holding his nerve to down Zverev and secure his first Hamburg Open title. In his post-match interview, he explained that he was serving underarm because he was cramping up when trying to serve normally.

"I'm really happy about how I played," said Fils. "I did everything for winning this match. I got cramps, when I was serving I was cramping. I was trying underarm serves because I cannot serve. The crowd took it badly but I don't care, I'm winning and that's it.

"Sascha [Zverev] is such a great champion. He's such a great champion playing unbelievable tennis. I knew from the start that it wasn't going to be easy. I was taking care of it in the first set. I had a bit of luck but I was playing great, then he managed to play better and raise his level in the second set.

"When they closed the roof I knew it was going to be a dogfight. I just had to fight until the last ball. I've been practicing for a long time for these moments, so I'm really happy."

The two players shared a frosty handshake after the match but Zverev went on to show class in defeat by congratulating Fils on his hard-fought victory.

"Arthur and your team, well done," said Zverev, who was the defending champion after winning last year's edition of the tournament. "Great week and you deserve your title. Enjoy the moment."