British number one Andy Murray suffered a heavy defeat as he was swept aside 6-1 6-2 by Stanislas Wawrinka in the third round at the Monte Carlo Masters.
Murray, who had won eight of his previous 12 meetings with the world number 17, looked far from his best as Swiss Wawrinka punished his tame serve.
The defeat, in his second match on clay this year, is a blow to Murray's preparations for May's French Open.
Both Novak Djokovic and Rafael Nadal progressed to the last eight.
Murray climbed to second in the world rankings with victory over David Ferrer in the final of Miami's Sony Open at the end of March and, despite tending to make a slow transition to the clay-court season, had hoped to close the gap on world number one Djokovic in Monaco.
But as a result of this defeat he will again fall behind Roger Federer.
"Twenty-four unforced errors is far too many - a set's worth," said Murray after his disappointing defeat.
"That's where half the points went. I started making a lot of errors - he was able to dictate all of the points from there."
Murray is next scheduled to play at the Madrid Open, which begins on 5 May, before competing in Rome in his final event before Roland Garros.
"I've had tough losses on the clay before and I've come back well from them. Hopefully today will be the same,'' he added.
The Scot, who has reached the last four of the Monte Carlo Masters only twice in his six previous attempts, rarely looked like making the semi-finals this year.
Murray, who comfortably beat 6-1 6-4 in his tournament opener, warned before his third-round tie that Wawrinka, who won only twice in 13 meetings with top-10 opponents last season, would pose a tough test.
Wawrinka had to save a break point in his opening service game but then exploited Murray's own wayward serve to break the US Open champion three times in succession and run away with the opening set.
The Swiss's momentum was unchecked in the second set as he closed out a hold to love with a pair of powerful serves to take the opener.
Murray showed resolve, if no upturn in form, to save a break point in staggering to 2-2, but he was soon undone by Wawrinka's power, volleying long to fall to 4-2.
A miserable afternoon's work was over for Murray as he netted a forehand to concede the second of two match points.
Wawrinka's victory was his third over a world number two after wins over Federer in the same tournament in 2009 and David Nalbandian in Basel in 2006.
The 28-year-old will face Frenchman Jo-Wilfried Tsonga in the next round.
Eight-time defending champion Nadal, meanwhile, will meet Grigor Dimitrov next after a 6-2 6-4 defeat of Philipp Kohlschreiber.
The Spaniard, 26, extended his winning streak in Monte Carlo to 44 matches with victory, while Bulgarian Dimitrov beat Florian Mayer 6-2 6-4 in the third round.
Djokovic, 25, had things tougher as he came from a set down to win for the second day in a row.
The Serbian beat Juan Monaco 4-6 6-2 6-2 to set up a quarter-final against Jarkko Nieminen, the Finn ousting Argentine Juan Martin Del Potro 6-4 4-6 7-6 (7-4).
Fourth seed Tomas Berdych was also a surprise casualty, beaten 6-4 6-2 by unpredictable Italian Fabio Fognini.