An out of sorts Benoit Paire crashed out of the Los Angeles Open as the top seed's eccentric game culminated in a 7-5, 6-4 opening loss to American Michael Russell.
Paire, ranked 50th in the world, on Thursday committed 38 unforced errors while losing his serve five times in the first set. The Frenchman also failed to sit down on several changeovers, often holding his right abdomen.
Other times he applied ice to the area and he fired eight double-faults - three in one game - to keep the contest off-balance throughout.
French fourth seed Nicolas Mahut was more stable, booking his second quarter-final of the season by beating Italy's Paolo Lorenzi 7-5, 7-6 (9/7).
"I knew it would be a difficult match," said 30-year-old Mahut. "I just beat him in the Wimbledon first round. Breaking in the first set to win was the key. After that I got more confident. I am happy to go through."
Mahut saved two set points in the second set before closing it out on a Lorenzi volley error.
Russell, ranked 83rd, said that he faced a mental and physical battle against the unpredictable Paire.
"It was extremely difficult, You never know what to expect from him. He keeps you out of your rhythm.
"I had to dig deep to get through it. He's flashy and sometimes looks like he's not trying. Mentally it's difficult, but I'm proud of myself for winning. I couldn't ask for a better start, I love playing on the hard courts."
Xavier Malisse advanced after some last-minute changes to his serve which the fifth seed used to overpower Aussie Matthew Ebden 6-4, 6-3.
Malisse, who is into his third quarter-final at the UCLA campus facility, had snapped a losing streak here going back to 2005 when he won his opening match on Tuesday.
The last-minute technique changes resulted in a superlative 90 per cent average on first serves, an instant dividend for the 32-year-old ranked 72nd in the world.
"We've been working on changing my serving," said Malisse, who will next play two-time champion Sam Querrey of the US, the second seed.
"We only really changed it this morning, but I worked on it a bit in doubles (Wednesday). I'm turning my foot a bit more on the court to get more power.
"It seems to be working," said the winner, who advanced with eight aces in a 73-minute win which also featured 22 winners and three breaks of serve against Ebden, a quarter-finalist last week in Atlanta.
"I guess I have a new weapon. In tennis you can always learn new stuff, but you have to be open to change. That's the only way you can get better. Hopefully I can keep serving like this."
Veteran Malisse improved his record at the Los Angeles event to 9-8, with one more win on Friday putting him into only his second semi-final since his debut 11 years ago in 2001.
The Belgian, who won his last ATP title five years ago, also moved past break-even for the season with an 18-17 match mark.
Aussie Marinko Matosevic, the sixth seed, defeated Germany's Tobias Kamke in a momentum-shifting 6-3, 1-6, 6-0 win. Qualifier Richard Berankis of Lithuania reached the last eight with a defeat of Russian Igor Andreev 6-4, 7-5.