Sam Querrey won his 11th consecutive match at the Los Angeles Open, spending just 36 minutes on court to post a 6-2, 3-1 quarter-final win as Xavier Malisse retired with an injury.
The Belgian fifth seed Malisse on Friday had to quit with a knee injury which had bothered him since the start of the hardcourt tournament at the UCLA venue.
The easy passage gives two-time winner Querrey, of California, a Saturday semi-final against compatriot Rajeev Ram, who upset Argentine third seed Leonardo Mayer 7-6 (7/3), 6-3.
In the other semi-final at the UCLA venue, sixth seed Marinko Matosevic of Australia will face Lithuanian qualifier Richard Berankis.
French fourth seed Nicolas Mahut lost 6-4, 6-4 to fourth seed Berankis. The Frenchman was unable to keep a clean slate against the 22-year-old after beating him last summer.
Matosevic defeated Michael Russell 6-2, 6-3 a day after the 34-year-old put out French top seed Benoit Paire.
Querrey had a huge day on serve in his abbreviated match, losing just one point on his serve in the 22-minute opening set. The second set lasted only 14 minutes before the 32-year-old Malisse packed it in.
"It was a good win for me, but I'm sorry Xavier had to quit," said the winner, who has not lost a Los Angeles match in five years. "I was serving great for the set and a half that it lasted.
"I just love playing at home in front of my family and friends."
World number 57 Querrey improved to 12-2 at the venue and won his 16th match of the season. A year ago he missed the event as he recovered from elbow surgery.
The Querrey-Ram semi-final will guarantee an American in the final for the sixth straight year.
The pair have met three times on the ATP, with Querrey winning the last two.
"I'll have to serve this well again," said Querrey. "Rajeev has a unique game, he likes to serve-volley and I'll have to be ready for that."
World number 66 Mahut, 30, stands 15-14 on the season, with his best result being a Montpellier quarter-final in February.
Mahut exited in just under 90 minutes as he lost serve once per set to the eager challenger.
"It was a great match for me, we both played well," said Berankis. "I was lucky on some returns. Somehow I won today, I'm really happy about it."
Berankis is the first Los Angeles qualifier in three years to get this far, following in the footsteps of Australian Carsten Ball in 2009 when Ball lost in the final.
Ram will be playing in his second semi-final this month after a strong performance at Newport on grass the week after Wimbledon. He rallied from 3-1 down in the second set, winning the last five games to advance over Mayer.
"I got a bit negative. I didn't want to do that so I told myself to stay positive," said Ram. "I want to keep riding the wave and keep doing well here.
"I'm feeling really good about my game. I've been doing well lately, and I just hope to keep it going. I just had to concentrate to hold my own serve, that was the key to the match."
