Nishikori, Lu advance, Hewitt out at Memphis
Kei Nishikori of Japan, pictured during an ATP tournament in Tokyo, on February 2, 2014 - by Toshifumi Kitamura
Nishikori battled back to defeat Russian Alex Bogomolov 3-6, 6-3, 6-2 to book a last-four berth against Russell, who downed Hewitt 6-3, 7-6 (8/6), taking his first victory in four career meetings with the Aussie in one hour, 48 minutes.
Taiwan fourth seed Lu Yen-Hsun also advanced, ousting US qualifier Alex Kuznetsov 6-1, 6-4 in 74 minutes to reach a semi-final against the winner of a later match between American Jack Sock and Croatia's Ivo Karlovic.
Nishikori, an ATP top seed for the first time, saved all four break points he faced in the final set to win after two hours and 18 minutes.
"It wasn't easy," Nishikori said. "My tennis level is not quite 100 percent yet, so I hope I can get better. I have a lot of confidence and my goal is to win the tournament."
Nishikori, ranked 16th, has never before played Russell, who is ranked 98th and has never won an ATP title.
Bogomolov, aged 30 and rated 80 spots below Nishikori is also seeking his first ATP title, and he broke Nishikori's first two service games for a 4-0 lead.
Nishikori broke back in the seventh game but Bogomolov held in the ninth to take the first set.
The second set featured two early exchanges of breaks before Nishikori held for a 4-3 edge, then broke the Russian and held again to force a third set.
Nishikori, 24, broke for a 2-1 edge and again to seize command before fighting off the Russian's final break chance in the last game.
"His ranking might not be top 50 but he can play," Nishikori said.
Nishikori, who won two singles matches and shared a doubles triumph to spark Japan over Canada in Davis Cup play earlier this month, is seeking his fourth career ATP crown.
His titles came as a teen at Delray Beach in 2008, at Tokyo in 2012 and last year at Memphis when he dispatched Spain's Feliciano Lopez in the final.