John Isner will play Thomaz Bellucci in the first reverse singles match on Sunday.
Robredo beat John Isner 6-7 6-3 7-6 after Sanchez saw off American Melanie Oudin 6-4 6-4.
Maybe this is the year John Isner barrels into the semis of a major.
The next highest-ranked Americans are Andy Roddick at 14 and John Isner at 18.
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Despite the defeat, Querrey is certain to usurp John Isner as the U.S.'s top-ranked male tennis player.
Elsewhere, U.S. star John Isner faces a race against time to be fit for the Australian Open.
Ferrer was followed on court by Nicolas Almagro and John Isner who played out a thrilling five-set match.
Second seed Nadal reached the quarterfinals for a sixth successive year after beating 13th-seeded American John Isner 7-5 6-4.
Ljubicic goes on to face David Ferrer in the last four, while Novak Djokovic will play qualifier John Isner.
Kevin Anderson beat John Isner in straight sets to draw the South Africans level before the concluding mixed doubles.
The winner of that match will play either big-serving American second seed John Isner or Swiss No. 4 Stanislas Wawrinka.
Roddick retired during last year's U.S. Open, on his 30th birthday, and now John Isner is America's No. 1 player.
Llodra ovecame 10th seed John Isner 6-4 7-6 (7-5) to end the American's hopes of making it through to London.
Roger Federer breezed past John Isner 6-3 6-4 while Novak Djokovic eased to a 6-3 6-3 victory over Ivan Ljubicic.
Elsewhere, John Isner won his career title after overcoming Spain's Nicolas Almagro in the final of the U.S. Clay Court Championship.
American 16th seed John Isner survived another marathon match as he defeated 2006 semifinalist David Nalbandian 4-6 6-3 2-6 7-6 (7-5) 10-8.
Wawrinka, the 18th seed, won 6-4 7-5 against Australian veteran Lleyton Hewitt, who on Saturday beat last year's losing finalist John Isner.
John Isner can seal America's place in the semi-finals if he beats the French No.1 Jo-Wilfried Tsonga in the first singles rubber.
Australian Leyton Hewitt also eased past big-serving American John Isner 6-2 6-4.
Murray will play Radek Stepanek after the Czech beat American John Isner 6-4 6-7 6-3 in a showdown of the big servers.
Roddick's fellow-American John Isner also reached the second round in Shanghai after saving match points in two tie-breakers against Polish qualifier Lukasz Kubot.
Then, of course, there was the 11-hour, five-minute circus act, performed over three days, by John Isner and Nicolas Mahut at Wimbledon in 2010.
Fish has dropped out of the world's top 10 after health problems, and is the second-highest ranked American at No. 20 after John Isner.
Jo-Wilfried Tsonga beat John Isner 6-3 6-2 to put France ahead before Williams fought off Mathilde Johansson 3-6 7-5 6-4 to draw the U.S. level.
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American John Isner , the No. 8 seed, won the a tight contest with fellow big-hitter Kevin Anderson of South Africa, winning 7-6 6-7 7-6.
American John Isner served up 20 aces as he stunned French third seed Jo-Wilfried Tsonga 4-6 7-6 (7-2) 7-6 (7-4) despite a brief break for rain.
But the United States hit back to level the tie as big-serving John Isner fired nine aces in a straight-set 6-3 6-2 7-5 win over Gilles Simon.
Murray will meet Tomas Berdych in the fourth round on Sunday after the Czech Republic 15th seed enjoyed a straight-sets win over American John Isner, ranked 17.
The Grand Slam record for a men's match is 11 hours, 5 minutes, an epic battle between John Isner and French opponent Nicolas Mahut at Wimbledon last year.
Two years after winning the longest match in grand slam history, No.10 John Isner was at it again as he faced France's Paul Henri-Mathieu in a marathon encounter.
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