NEW YORK (AP) Serena Williams took a medical timeout to have her right ankle re-taped and later double-faulted on the last two points as she and sister Venus lost in the doubles quarterfinals at the U.S. Open.
The Williams sisters, owners of 13 Grand Slam doubles titles, were beaten 7-6 (5), 6-4 Tuesday by the fourth-seeded Russian duo of Ekaterina Makarova and Elena Vesnina.
Serena's serve was broken early in each of the first two sets, and then again in the final game.
She and Venus are 4-3 in doubles in 2014, with two of the losses against Makarova and Vesnina. They also played each other at Dubai in February.
In singles, the top-seeded Serena and 17th-seeded Makarova could face each other again in the semifinals. They play their quarterfinal matches in that event Wednesday, with Serena - who has dropped only 17 games through four rounds - meeting 11th-seeded Flavia Pennetta, and Makarova taking on 16th-seeded Victoria Azarenka.
Serena is trying to become the first woman with three consecutive U.S. Open singles titles since Chris Evert won four in a row from 1975-78.
During the changeover at 2-1 in the second set of doubles, Williams removed her right shoe and sock while being visited by a trainer during a medical timeout.
The Williams sisters declined to speak to the media after the doubles match, but Serena told a WTA spokesman that she simply needed to have the tape on her right ankle redone and there was no injury issue.
The Williams sisters have not been to a major semifinal in doubles since losing in that round at last year's U.S. Open. Their last Grand Slam doubles trophy came at Wimbledon in 2012.
When they played together at Wimbledon this year, they stopped after three games in the second round on July 1, after Serena served four consecutive double-faults. She had looked disoriented during warmups, having trouble grabbing tennis balls tossed to her by ballkids. The reason given that day was that she was ill.
Williams did not speak about that episode at the time, but at a tournament at Stanford, California, nearly a month later, she acknowledged it scared her in retrospect.
''I didn't realize how I felt until later. In the moment I didn't realize how sick I was,'' she said in late July. ''It's weird but that's the fight in me. I never know when to say when.''
Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrich