JOIN USNovak Djokovic suffered a surprise defeat in his latest comeback from injury after the Serb was beaten by Martin Klizan in his first match at the Barcelona Open on Wednesday.
Djokovic had been due to meet Rafael Nadal in the quarter-finals in Spain but a disjointed display gave Klizan, ranked 140th in the world, a 6-2, 1-6, 6-3 victory.
While Klizan goes through to meet Spanish clay-court specialist Feliciano Lopez in the last 16, Djokovic will now have to reset, with the French Open next month fast approaching.
Kei Nishikori retired during his opening match against Spain's Guillermo Garcia-Lopez.
Nishikori, who lost to Rafael Nadal in the Monte Carlo Masters final on Sunday, pulled out after conceding the first set to Garcia-Lopez 6-3.
Fatigue, and pain in his troublesome right wrist, appeared to prompt the withdrawal from Japan's world number 22, who will now look to regain fitness ahead of the French Open next month.
"My expectations grew in Monte Carlo, despite losing to Nadal," Nishikori told reporters after the match.
"However, I started feeling discomfort again during the first set and I did not want to take any risks."
Wozniacki cruises
World number two Caroline Wozniacki powered past Russia's Ekaterina Alexandrova 6-2, 6-2 to reach the second round of the Istanbul Cup on Tuesday.
Denmark's Wozniacki was barely troubled by world number 101 Alexandrova as she converted five out of six break points to win her first clay court match of the season in 68 minutes.
Earlier, world number 54 Donna Vekic advanced after Agnieszka Radwanska retired due to a back injury. Croatia's Vekic was leading 6-1, 2-0 when third seed Radwanska said she could not continue.
Zhang Shuai was stunned by Dutch qualifier Arantxa Rus 6-2, 6-3 while Kazakhstan's Yulia Putintseva fought back to get past sixth seed Sorana Cirstea 0-6, 6-1, 6-0.
Seventh seed Irina-Camelia Begu saved four set points in the opening set before moving past Slovenian qualifier Dalila Jakupovic 7-5, 6-0. She meets America's Christina McHale next.