Dudi Sela is still searching for his first victory since July after losing 4-6, 6-1, 6-4 to qualifier Marco Chiudinelli in the first round of the Japan Open in Tokyo on Monday.
The 24-year-old Israeli, who fell one place to No. 44 in the world earlier Monday, has struggled desperately in the past two months, losing seven straight matches, including his defeat on the first day of the Davis Cup semifinals against Spain.
Perhaps the most worrying part of Sela's recent losing streak is the fact that in five of the seven defeats, including the loss to Chiudinelli (ranked 100th), he has succumbed to lower-seeded players.
Sela's search for his next elusive win will take him to China next week, where he will play in the lucrative $5,250,000 Shanghai Masters.
In other first-round action from Tokyo, Stanislas Wawrinka of Switzerland defeated American John Isner 6-4, 6-4.
Seventh-seeded Wawrinka converted five of seven break point opportunities in the match that lasted one hour, 33 minutes at Ariake Colosseum.
Germany's Simon Greul defeated Martin Vassallo Arguello of Argentina 4-6, 6-4, 6-2. He will face Wawrinka in the second round.
Top-ranked Roger Federer pulled out of the $1.2 million event, citing fatigue, along with third-ranked Andy Murray of Britain, who withdrew because of a wrist injury.
Fifth-ranked Juan Martin del Potro, the U.S. Open champion, is top-seeded in the singles draw and will play his first match on Tuesday against qualifier Edouard Roger-Vasselin of France. Tomas Berdych of the Czech Republic is the defending champion.
Meanwhile, world No. 1 Dinara Safina was beaten 7-5, 7-6 (5) by local wild card entrant Zhang Shuai in the China Open's second round on Monday, a shock defeat that could lead to the Russian's top ranking passing over to No. 2 Serena Williams.
In other drama, Venus Williams fell to Russian teenager Anastasia Pavlyuchenkova, whose 3-6, 6-1, 6-4 victory was her second over the American in a week, while Novak Djokovic fired 10 aces in a 6-3, 7-5 win over Romania's Victor Hanescu to advance to the second round.
On Tuesday, world No. 2 Rafael Nadal and defending China Open champion Andy Roddick begin their campaigns in the men's draw.
Having lost the first set to the 20-year-old Zhang, Safina found herself 5-4 behind in the second. She battled back to force the tiebreak, but with the crowd and momentum behind the local player, Zhang held firm.
According to the points reckoning, Safina would lose her No. 1 ranking to Serena Williams if she finished behind the American, who won her first round match Saturday against Estonia's Kaia Kanepi and next faces Russian Ekaterina Makarova on Tuesday. Safina can hold on to the top ranking if Serena loses.
The latest defeat comes a week after Safina was knocked out of the Toray Pan Pacific Open early by 18-year-old qualifier Chang Kai-chen from Taiwan.
Zhang, ranked 226th in the world, said close losses in the past to high-ranking players gave her confidence that she could win at their level.
"I woke up this morning feeling really excited, but didn't do any special preparation and never expected to win the match," she said.
However, Safina, who racked up 13 double faults, was also "not in the best condition and made too many errors," Zhang said.
Safina, who had begun shouting and growing visibly more distraught toward the end of the match, did not speak to reporters.
AP contributed to this report