Kei Nishikori was walking past Marinko Matosevic, ready to switch ends after winning the first set 6-4. The Australian stopped him near the umpire's chair.

Matosevic couldn't continue, not with a bone bruise in his right foot making each step simply too painful.

Matosevic retired 37 minutes into his semifinal against Nishikori on Saturday, sending the Japanese player to the final of the U.S. National Indoor Championships. Nishikori called the quick end surprising because he didn't know Matosevic was injured.

"He was playing really well from the beginning and he broke my serve in the beginning 2-love," Nishikori said. "He was playing well, I thought. So I didn't think about he was retiring. Yeah, he's playing well this week. ... Things happen. But yeah, lucky for me to play just one set and feel fresh for tomorrow so I think it's good."

On Sunday, Nishikori will face Feliciano Lopez of Spain, a 6-2, 3-6, 6-3 winner over Denis Istomin of Uzbekistan. Lopez will be seeking his third title in his eighth career ATP final after a match he thought he had won with an ace — even preparing to shake hands with the chair umpire — only to replay the point because of a let ruling.

"In the old times, we had one guy on the net with a finger," Lopez said. "I don't know if it's more accurate or not. The system now with the machine you never know when it's real let or not."

Marina Erakovic of New Zealand won her first singles title Saturday night when Sabine Lisicki of Germany retired because of an illness in the last women's final in Memphis. The women's event, held in Memphis since 2002, is moving to Rio de Janeiro in 2013.

Erakovic lost this final to Sofia Arvidsson last year, and she took the first set Saturday night 6-1 in 27 minutes. During the break, Lisicki sat down and realized she couldn't continue.

"I just didn't have any energy left in the tank," Lisicki said.

Erakovic looked almost disappointed. The winner of seven doubles titles said she didn't realize Lisicki had been ill so she was shocked when the German retired and reacted as if on auto-pilot until she was handed the guitar-shaped trophy.

"I've dreamed of winning WTA titles when I was little and for it to happen, I can just describe it as happiness and relief. Now it's been three finals and to win one, I just want to do a little dance."

Nishikori will be looking for his third career title and first since winning in Tokyo last October. That's when he became the first Japanese player to win on home soil in that tournament's 40-year history.

The top Asian player in the ATP rankings at No. 22, the fifth-seeded Nishikori was the only seed to advance out of the quarterfinals here after he ousted top-seeded Marin Cilic of Croatia.

"It's a tough tournament here, so I understand anything happens," Nishikori said.

Matosevic had been experiencing pain in his right foot since January. The pain reached a new level Friday night after beating Alexandr Dolgopolov in three sets. Matosevic iced his foot for a few hours and found that even walking to a grocery store across from his hotel was painful.

The Aussie, the ATP's most improved player in 2012 as he jumped from No. 201 in 2011 to 49th, still tried to make it through his third appearance in an ATP semifinal.

Matosevic took the doughnut-shaped pad protecting his foot off before the match and led 2-0 before Nishikori broke back. Nishikori broke Matosevic again to go up 4-3. Matosevic then called for a trainer, who doubled up the padding on the Aussie's right foot. That simply made it too awkward.

All on a day when the tennis ball looked as big as a basketball to the Aussie, and Matosevic felt good except when Nishikori forced him to move to his left or right chasing down volleys.

"It's tough," Matosevic said. "I definitely felt like I could've won today, and then the bottom half, all the seeds dropping out, Istomin, Lopez, it feels like a big missed opportunity."

Nishikori served out and won the set in 37 minutes. Matosevic then retired. So Nishikori spent five more minutes hitting some balls just to get some practice in before the final.

"It's good that I 'm fresh," Nishikori said.