John Isner, fresh off a seventh ATP title, fired 19 aces Wednesday to beat Alex Kuznetsov 7-6 (7/2), 7-6 (7/4) at the ATP and WTA Washington Open.
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.
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.