WASHINGTON, July 29 (Xinhua) -- China's Peng Shuai and her partner Bethanie Mattek-Sands of the United States lost to Japanese pair Eri Hozumi and Makoto Ninomiya in straight sets in the women's doubles first round at the San Jose Open on Monday.

Peng and Mattek-Sands seemed out of sorts as they just battled for one hour or so before losing the match at 6-2, 6-4.

The Japanese duo won 74 percent on their first serve and broke Peng and Mattek-Sands twice in each of the two sets. Peng and Mattek-Sands only converted on one of the four breaking chances throughout the match.

The San Jose Open, one of the warmup tournaments in runup to the US Open, will end on August 4.