TOKYO - Top seed Kei Nishikori withdrew from the Japan Open Wednesday due to a buttock muscle injury, disappointing home fans hoping he could recapture the trophy.
Kei Nishikori of Japan returns a shot against Joao Sousa of Portugal during the men's singles second round match at the ATP Japan Open tournament in Tokyo on October 5, 2016
The world number five became the latest star to pull out of the injury-plagued tournament, after US Open winner and defending champion Stan Wawrinka withdrew due to a back injury.
Nishikori retired during the first set of his second-round match against João Sousa of Portugal, ranked 34th in the world.
Going into the match, Nishikori looked to be in solid shape, comfortably building a 3-0 lead as he made his rival run back and forth across the hard court at Ariake Colosseum.
But the 26-year-old requested a medical timeout, asking his trainer to massage the left side of his lower back.
Resuming the match, Nishikori was clearly a different man, grimacing at times, although he managed to hold his service game to make it 4-0 before his legs gave up.
Sousa quickly made it 4-3, and Nishikori was forced to withdraw 41 minutes into the match.
The Japanese star, title winner in 2012 and 2014, voiced disbelief at the outcome.
"Until a second ago, I was feeling really good and made it 3-0" before things deteriorated, he told a press conference after the match.
"I still cannot believe what happened."
Sousa will now play against Belgian fifth-seed David Goffin, who defeated Jirí Veselý of the Czech Republic 6-3, 7-5.
Fourth-seed Marin Cilic also defeated Spaniard Fernando Verdasco 4-6, 7-5, 7-5 in the second round.
Gilles Muller of Luxembourg advanced to the second round by defeating Czech third-seed Tomas Berdych, winning the first set in a tie break before dominating the second set to claim victory 7-6 (9/7), 6-1.
Berdych also asked for a medical timeout in the second set, but stayed on to finish the match.