Andy Murray suffered a first loss on grass since 2012 after seeing preparations for the defence of his Wimbledon title stall with defeat to Radek Stepanek in two sets at the AEGON Championships at Queen's Club.
Stepanek stormed into the quarter-final meeting with Kevin Anderson with a 6-4 6-2 victory over the defending champion, playing his second match under the guidance of new coach Amelie Mauresmo.
After strolling past Paul-Henri Mathieu on Tuesday, Murray was expected to make short work of his Czech opponent but saw eight set points come and go in the first set tie-break as Stepanek grabbed the ascendency.
And after grabbing two breaks, the world No.40 prevailed in straight sets as Murray was unable to raise his game as his 19-match unbeaten run on grass came to an end.
Though only in the early stages of his partnership with Mauresmo during the summer's grass court season, such an emphatic defeat will draw scrutiny over the relationship ahead of the defence of Murray's Wimbledon crown which begins in less than a fortnight.
"The way I played today I was very happy to serve well against one of the best returners in the game," said Stepanek. "The first set tie-breaker was certainly important.
"When you pay the best players in the world you have to come up with your best and it brings the best out of you and today was an example of that."