Japan's Kei Nishikori and Feliciano Lopez of Spain will meet in Sunday's final at the $1.212 million U.S. National Indoor Tennis Championships.
The fifth-seeded world No. 22 Nishikori was leading Marinko Matosevic by a 6-4 margin when the Australian retired with a bone bruise on the bottom of his right foot.
In the other semifinal on Saturday, Lopez took down Uzbekistan's Denis Istomin 6-2, 3-6, 6-3 at The Racquet Club of Memphis.
Lopez has a 2-5 record in title matches, and will be hoping to claim his first title since 2010. Meanwhile, Nishikori has a 2-2 record in finals, winning his biggest title to date on home soil last October in Tokyo.
The 2013 Memphis champ will claim $291,800.