Stan Wawrinka showed glimpses of his Grand Slam winning form but was bundled out of the Fever-Tree Championships by former Queen's Club champion Sam Querrey on Wednesday.
The Swiss squandered seven set points in the opener and although he took the second on a tiebreak he capitulated in the decider after dropping serve at 1-2, losing 7-5, 6-7(3), 6-1.
His frustration boiled over when he hit a backhand long to hand Querrey the break and he buried his racket frame into the lush centre court turf, taking a sizeable divot in the process, before snapping it over his knee.
Big-serving American Querrey, champion in 2010, calmly ticked off the next three games to move into the quarter-finals where he will meet top seed Marin Cilic, who fought back to beat Luxembourg's Gilles Muller 4-6, 6-3, 6-3.
Wawrinka's ATP ranking has plummeted to 261 after his first-round loss at the French Open, having reached the final a year ago, but the good news is that his knees appear strong again after two surgeries last August.
He struck the ball with authority in the second set and played a solid tiebreak but his lack of sharpness told as he was sent packing by the fifth seed.
He was left to rue the 10th game of the first set when Querrey saved a succession of set points before winning eight of 10 points from 5-5 to take the opener.
"It's for sure some frustration to lose it, but I have to look at it the right way," Wawrinka told reporters.
"I think the level is there. I think I'm moving quite good on the grass. I was feeling good."
Querrey, who fired down 25 aces on his way to victory, joined fellow American Frances Tiafoe in the last eight after he beat Argentine Leonardo Mayer 6-4, 2-6, 6-4.
Croatian Cilic, winner at Queen's in 2012 and runner-up last year, banged down 19 aces to Muller's 17 in a match of few long rallies and he can expect a similar firefight against Querrey.
Frenchman Jeremy Chardy maintained his impressive form on grass with a 7-6(6) 6-3 defeat of young Russian Daniil Medvedev.
Sugita stuns Thiem to reach Halle quarter-finals
Erratic serving cost Dominic Thiem dearly as the third-seeded Austrian suffered a 6-2 7-5 defeat by Japan's Yuichi Sugita in the second round of the Halle Open on Wednesday.
French Open runner-up Thiem double-faulted four times and landed only 53 percent of his first serves in play as he struggled to find his rhythm on the German grass.
World number 52 Sugita took his chances to break his seventh-ranked opponent three times, before clinching one of the biggest wins of his career in just under an hour and a half.
The result represents a setback for Thiem's Wimbledon preparations, with the Austrian having failed to progress beyond the last-16 in his four appearances at the All England Club.
Earlier in the day at Halle, big-hitting Russian Karen Khachanov overcame Japan's Kei Nishikori for the second straight year at the last-16 stage.
The 22-year-old Khachanov fired seven aces and broke his opponent's serve twice in each set to win 6-2, 6-2 in 78 minutes.
"I had to play more aggressive," Khachanov, recording his 20th match win of the season, said courtside.
"I had good memories here on centre court. I played three matches here last year so it gave me a lot of confidence and experience. This year has been great so far."
Khachanov will next face Spanish fourth seed Roberto Bautista Agut, who overcame Dutchman Robin Haase 6-4 7-5.