Third seed Lleyton Hewitt suffered a shock straight-sets loss to American Michael Russell on Friday at the ATP US Indoor Championships in Memphis.

Russell beat Hewitt 6-3 7-6 (8-6) in their quarter-final showdown, his first victory in four career meetings with the Australian, in one hour and 48 minutes.

Defending champion Kei Nishikori rallied to reach the semi-finals, battling back to defeat Russian Alex Bogomolov 3-6 6-3 6-2.

Nishikori, an ATP top seed for the first time, saved all four break points he faced in the final set to win in two hours and 18 minutes.

“It wasn’t easy,” Nishikori said. “My tennis level is not quite 100 per cent yet, so I hope I can get better. I have a lot of confidence and my goal is to win the tournament.”

The world No.16 has never played Russell before. The American is ranked 98th and has never won an ATP title.

Taiwan fourth seed Lu Yen-Hsun and American Alex Kuznetsov were to meet in a later quarter-final with that winner to face American Jack Sock or Croatia’s Ivo Karlovic in the last four of the $US647,000 ($A724,000) tournament.

Bogomolov, rated 80 spots below Nishikori and still seeking his first ATP title at age 30, 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 lead 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, seeks his fourth career ATP crown.

His titles have come 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.