Top seed Kei Nishikori has marched into the semi-finals of the Memphis Open as he looks for a fourth straight title at the event.

Japanese world No.7 Nishikori breezed past Kazakh world No.93 Mikhail Kukushkin 6-2 6-4 in just over 90 minutes to book a semi-final showdown with American Sam Querrey.

The scoreline belied the pressure Nishikori was under at times, but he played the big points well, saving all five break points he faced to record a 15th-straight match win in Memphis.

He now meets the big-serving Querrey, who earlier pushed aside Japanese qualifier Yoshihito Nishioka 6-3 6-4.

Querrey one of two Americans into the semis – the first one through, 18-year-old wildcard Taylor Fritz creating a piece of history on his way.

Fritz beat Benjamin Becker of Germany 6-4 5-7 7-6 (7-5), becoming the youngest American to reach an ATP semi-final since 1989.

Fritz, who turned 18 on October 28, used his big serve and strong forehand to advance to his first career ATP semi as the youngest American to do so since Michael Chang won Wembley in 1989 at the age of 17

“It feels incredible,” Fritz said.

“You know it’s a great milestone. I always say this is reassuring to know that I’m doing the right thing and I’m on the right track.”

The teenager will play Ricardas Berankis of Lithuania on Saturday.

Berankis upset third seed Donald Young 7-6 (7-3) 6-1 in their quarter-final match.