Rafael Nadal is counting on antibiotics to control his appendicitis so he can get through the Shanghai Masters this week.
The second-ranked Nadal began feeling pain in his abdomen late Saturday, and the next day went to the hospital where he learned he had the early stages of appendicitis.
Nadal said on Tuesday he chose to try treatment with antibiotics rather than undergo surgery right away. He felt well enough to begin hitting again, he said.
The 14-time major winner said the risk of his condition getting worse after three days of steady improvement "is always very, very low."
"I am not going to go for surgery. That's great news for me today. That's why I'm here practicing for 45 minutes, and trying to play tomorrow. But obviously I am not in my best condition," he said.
Nadal said he will talk with his doctors when he returns to Spain after the tournament about whether he will need to have the appendix removed.
The Spaniard is playing just his second tournament since returning from a two-month layoff due to a wrist injury. After missing the summer hard-court season, including the defense of his title at the U.S. Open, Nadal said it was important to get back on the court as soon as possible so he's back in top form before the Australian Open in January. He reached the China Open quarterfinals last week.
Nadal plays his opening match on Wednesday against countryman Feliciano Lopez.
Top-seeded Sam Stosur began the defense of her Japan Women's Open title in Osaka with a straight-sets victory against Misa Eguchi of Japan.
Coming off a semifinals run in the China Open last week, Stosur defeated Eguchi, 6-4, 7-5. She will face Australian Jarmila Gajdosova in the second round. The three other seeded players in action also won; No. 4 Coco Vandeweghe beat Kristina Mladenovic of France, 6-2, 6-3, No. 5 Zarina Diyas of Kazakhstan topped qualifier Chan Yung-jan of Taiwan, 7-6 (3), 6-1, and No. 8 Lauren Davis of the United States beat qualifier Hiroko Kuwata of Japan, 1-6, 6-4, 7-6 (3).