Eighth-seeded American Isner, who won last week at Atlanta, advanced to the round of 16 at the $1.76 million hardcourt event before rain washed out most of the day´s matches.[break]
That included tournament openers for Argentine top seed Juan Martin Del Potro, the 2009 US Open champion and a two-time Washington winner, and second seed Kei Nishikori, who received first-round byes.
Two other second-round matches were halted, with South African seventh seed Kevin Anderson leading Australian qualifier James Duckworth 6-3, 3-6, 5-4 and German third seed Tommy Haas leading US qualifier Tim Smyczek 3-6, 7-5, 1-0.
The total washouts for Nishikori, ranked a career-best 11th this week, and Del Potro mean they will have to win five times in four days to take the title.
Thursday´s schedule has both players slated for two matches.
That bolsters Isner´s hopes for back-to-back trophies, despite a tough title run last week.
Big-serving Isner won six of seven tie-breakers he played in Atlanta, but dropped one to Anderson in the final and only won the last-set tie-breaker after saving two match points.
"The tank isn´t completely full, but I´ve got a lot of confidence," Isner said. "I´ve been able to focus and play well in the tight moments. Using my weapon, my big serve, puts a lot of pressure on opponents.
"I feel like I can get sharper as this event goes along."
Isner will play India´s 129th-ranked Somdev Devvarman on Thursday for a spot in the quarter-finals. They last played in the 2007 US college finals when top seed Isner was an upset loser.
"Somdev is a great player and a good friend," Isner said. "I knew eventually our paths would cross (as pros). It will be a fun match. I´ll need to play very well."
Mardy Fish, who has missed much of the past year with heart problems, ousted French 13th seed Julien Benneteau 6-3, 7-5 for his 299th career ATP match victory.
"It was a good test to see where I was," Fish said. "It was a good test passed."
The 64th-ranked American´s back-to-back wins are his first since March.
On the women´s side, Germany´s Andrea Petkovic upset sixth-seeded compatriot Mona Barthel 6-2, 6-2 to reach the last eight in the only match completed.
"I was happy to get off to a great start and keep it up," said Petkovic, who has been nagged by injuries so much this season that being near 100 percent "is a nice feeling I almost forgot about."
Petkovic said that she was so happy to be healthy and playing again that "even the losses don´t hurt as much as they used to."
Three other second-round matches were postponed to Thursday, including German top seed Angelique Kerber´s meeting with American Melanie Oudin.
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