Kei Nishikori retired from his quarterfinal against top seed Novak Djokovic on Wednesday, succumbing to an injured thigh as he trailed 6-1, 4-1.
Nishikori, ranked ninth in the world, was coming off a five-hour, five-set match on Monday and could not keep up with the world No. 1, who was also coming off a tough fourth-round match.
"This is just what the doctor ordered," Djokovic said.
"It's hard to win like this, especially against Kei. We've played a lot of matches against each other. I hope it's not too serious and he has a speedy recovery," he added.
Nishikori made five unforced errors en route to dropping his serve in the second game, while winning just one point across Djokovic's first two service games. Trailing 4-1, Nishikori was stung by a pair of double faults and was flexing his right thigh on court.
"I felt pain in my right thigh when I was serving. Most movements became painful," said Nishikori, who called for a trainer as soon as the first set ended, with 19 unforced errors on his ledger.
After returning to action, Nishikori opened the second set by easily winning his first service game but then surrendered 12 straight points to fall behind 3-1. He called it quits after dropping his next service game.
Nishikori, who last beat Djokovic in the semifinals of the 2014 U.S. Open, fell to 2-16 in his career against the Serb.
Djokovic next faces 28th seed Lucas Pouille in the semifinals.