Top-seed Kei Nishikori defeated defending champion Peter Gojowczyk 7-6(4), 6-3 in his opening match of the Moselle Open on Wednesday to book a place in the quarterfinals.

Playing for the first time since his semifinal exit at the U.S. Open, Nishikori struggled early against the German and was unable to break his opponent's serve in the first set on the indoor hardcourt at the Arenes de Metz.

But after winning the tiebreaker 7-4, he managed to turn the game, breaking Gojowczyk twice in the second set to claim victory in 1 hour, 33 minutes at the ATP World Tour 250 Series event.

"I had trouble handling his flat balls," Nishikori said.

"I had to play defensive tennis and it was a tough match. I gradually got better in the second set. (Victory in) this tournament is key in order to boost my confidence," he said.

The 28-year-old Japanese, currently No. 12 in the world, is looking to qualify for the ATP Finals for the first time since 2016 and fourth time in his career.

The world's eight best men's singles players and doubles teams compete for the prestigious year-end title at the tournament which will be held Nov. 11-18 at the O2 Arena in London.