Fifth seed Andy Murray, sixth-seeded David Ferrer and defending champion Ivan Ljubicic all fell by the wayside on a day of startling upsets at the Indian Wells ATP tournament on Saturday.
British world number five Murray was eliminated 7-6, 6-3 by American qualifier Donald Young, Spaniard Ferrer crashed out 7-6, 6-3 at the hands of Croat Ivo Karlovic and Ljubicic was beaten 5-7, 6-4, 6-2 by Argentine Juan Martin del Potro.
The early exit of Murray was the most surprising, despite the fact that the 23-year-old Scot had not competed in more than a month.
Murray has always enjoyed playing at Indian Wells, where he was a runner-up in 2009, but he struggled for fluency against his 143rd-ranked opponent who won the biggest match of his career with an aggressive brand of tennis.
"Most of it was not great today," Murray told reporters after being beaten in just over an hour-and-a-half.
"I didn't serve particularly well, I didn't move very well. He hit a lot of winners and gained in confidence, I guess, from hitting more winners," he added.
Karlovic, whose 2010 season was cut short by six months due to Achilles surgery, powered down nine aces before sealing victory against Ferrer in 95 minutes.
The six-foot 10-inch (2.08 metre) Croat won the first set tiebreaker 7-3 and then broke his opponent in the fourth game of the second before fittingly ending the match with an ace.
"I was playing well, I was returning well and I played good on my second serve, which this year has not been the case," Karlovic said.
"But I began to play better and better and today was really good," he added.
Ranked a lowly 239th, the 32-year-old Croat improved his win-loss record for the year to 4-7 with his first victory against world number six Ferrer in three meetings.
Karlovic, who broke the fastest serve world record with a 251 kph (156 mph) blast during his country's Davis Cup tie against Germany in Zagreb last week, will next meet either Frenchman Gilles Simon or German Rainer Schuettler.
Croat Ljubicic, who upset American Andy Roddick 7-6, 7-6 in last year's final, won a tight opening set against del Potro before being broken once in the second and twice in the third.
"It was not an easy draw, of course," Ljubicic said of his opponent, a former world number four who played just three tournaments last year because of an injury to his right wrist.
"He's a great player and it was a great match. We had some great points and I came up short in the end. Del Potro played a solid game, as normally he does, and it was too much for me today," he added.
Del Potro, who won his eighth ATP title at last month's Delray Beach International Championships, will next meet Ukrainian Alexandr Dolgopolov, a 6-4, 6-4 winner against Romania's Victor Hanescu.
In other second-round matches, India's Somdev Devvarman also delivered an upset with a 7-5, 6-0 victory over 19th-seeded Cypriot Marcos Baghdatis while Spaniard Tommy Robredo beat Germany's Mischa Zverev 6-3, 3-6, 7-5.
Ninth-seeded Spaniard Fernando Verdasco eased past Lithuania's Richard Berankis 7-5, 2-0, after his opponent retired hurt, and 23rd seed Albert Montanes of Spain scraped through 7-6, 2-6, 7-6 against Finland's Jarkko Nieminen.
Spanish world number one and top seed Rafa Nadal was scheduled to play his first match of the week at the ATP Masters 1000 event later on Saturday against South African qualifier Rik de Voest.
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