KEY BISCAYNE, Fla. -- Novak Djokovic advanced without hitting a ball for the second time at the Sony Open, and now he's in the final.
Djokovic received his latest walkover Friday when Kei Nishikori withdrew less than two hours before their semifinal because of a left groin injury.
"I tried to warm up and I couldn't move" Nishikori said. "With anybody on the other side, I don't think I could win today."
The No. 2-ranked Djokovic also got a walkover in the third round and has played only six sets in the tournament. He'll try for his fourth Key Biscayne title Sunday against the winner of Friday night's match between No. 1 Rafael Nadal and No. 7 Tomas Berdych.
No. 1 Serena Williams will try for her seventh Key Biscayne title when she plays No. 2 Li Na on Saturday.
Former No. 1 Martina Hingis advanced to her first doubles final since 2007 when she and Sabine Lisicki beat Cara Black and Sania Mirza 6-3, 6-4.
Nishikori said his groin has bothered him for more than a month, and he retired during a match in Delray Beach last month. This week he won a won a three-set match against David Ferrer, saving four match points, and then beat Roger Federer in a three-setter Wednesday night.
The No. 21-ranked Nishikori said he won't need surgery, but he's unsure how long he'll be sidelined and will fly home to Japan to see a doctor. His next scheduled match is in Davis Cup for Japan against the Czech Republic in Toyko on April 4.
Nishikori has retired or withdrawn 14 times in his career, including three times in Grand Slam events. He was hoping to reach his first ATP Masters 1000 final.
"It was going to be a great challenge for me today," Nishikori said. "Hopefully I can play another time."
A Key Biscayne men's semifinal was also cancelled in 2012 when Nadal withdrew because of a knee injury, giving Andy Murray a walkover.
Djokovic will try to complete a March sweep Sunday. He won the Indian Wells title two weeks ago, when he beat Federer in the final.
Regardless of results the rest of the week, Nadal will remain No. 1 and Djokovic No. 2 next week.