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 several set points in the opening set and although he took the second on a tiebreak, he capitulated in the decider after dropping serve at 1-2.
His frustration boiled over as he buried his racket frame into the lush centre court turf, taking a sizeable divot in the process, before snapping it over his knee.
And big-serving American Querrey, champion in 2010, calmly ticked off the next three games to seal a 7-5 6-7 6-1 win and move into the quarter-finals, where he will meet top seed Marin Cilic.
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 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.
Cilic maintained his mastery over Luxembourg's Gilles Muller, hitting back to win 4-6 6-3 6-3 in their latest big-serving battle.
Chasing his second Queen's title and his fourth final appearance, Cilic once again frustrated Muller 12 months after beating him in the final set in both the Wimbledon quarter-finals and Queen's semi-finals.
The Croatian, who lost last year's Queen's final against Feliciano Lopez, hit 19 aces to 17 from Muller as he made the quarter-finals for the seventh time.
Earlier, American prodigy Frances Tiafoe moved into his first ATP Tour grass-court quarter-final with a 6-4 2-6 6-4 win against Argentina's Leonardo Mayer.
Tiafoe, ranked 62nd, is looking to add a second ATP title to his maiden success at Delray Beach in February.
We have tennis coverage from the ATP Tour as Roger Federer bids for another title at the Gerry Weber Open in Halle. Watch the action live on Sky Sports Arena all this week.