Memphis, USA, 24 February 2013 | AP

A devastated Marinko Matosevic on Saturday was forced to retire injured in his semifinal against Japan’s Kei Nishikori at the US National Indoor Tennis Championships in Memphis.

The Australian had to pull out with a bone bruise in his right foot after losing the first set 6-4.

Fifth-seeded Nishikori was surprised when his Matosevic told him he couldn’t go on.

“He was playing really well from the beginning and he broke my serve in the beginning 2-love,” Nishikori said. “Things happen. But yeah, lucky for me to play just one set and feel fresh for tomorrow, so I think it’s good.”

With a heavy sigh, Matosevic described his withdrawal as a bittersweet moment.

“If you would’ve told me before the week I would make the semifinals, I’d take it. Today, the way I was seeing the ball and striking it, it’s tough.

“I definitely felt like I could’ve won today, and then the bottom half – all the seeds dropping out, (Denis) Istomin, (Feliciano) Lopez – it feels like a big missed opportunity.”

Nishikori will play Spain’s Lopez on Sunday, looking for his third career title and first since winning in Tokyo in 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 in the ATP rankings at No.22, Nishikori was the only seed to advance out of the quarterfinals 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 having pain in his right foot since January. The pain reached a new level on Friday after the adrenaline from beating Alexandr Dolgopolov in three sets in the quarterfinals.

Matosevic iced his foot for a few hours and found even walking to a grocery store across from his hotel painful.

The Aussie, the ATP’s most-improved player in 2012 as he jumped from No.201 in 2011 to 49th, still tried to play in only his third career ATP semifinal.

Matosevic broke Nishikori twice to go up 4-3. Matosevic then called for a trainer, who doubled up the padding on his right foot. That simply made it too awkward.

This was 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.

In the second semi-final, Lopez defeated Denis Istomin of Uzbekistan 6-2 3-6 6-3.