Top seed Juan Martin Del Potro and US eighth seed John Isner advanced to the final of the ATP and WTA Washington Open with rain-interrupted triumphs on Saturday.
Seventh-ranked Del Potro, the 2009 US Open champion from Argentina, defeated German third seed Tommy Haas 7-6 6-3 while Isner blasted 29 aces in a 6-7 6-3 6-4 victory over Russia's Dmitry Tursunov.
Del Potro, the 2008 and 2009 Washington winner, was down 1-4 when rain halted the first set for more than three hours, but won the next four games once play resumed, saved a set point with a second-serve ace in the 12th game and took the tie-breaker when Haas hit a backhand long.
Haas netted a backhand to surrender a break in the eighth game of the second set and Del Potro held for the victory, stretching his win streak to 13 matches at the $US1.76 million ($A1.98 million) hardcourt event, having not played in the US capital since his title run four years ago.
Haas fell to 0-5 against Del Potro and has never taken a set from the South American star.
Isner, who won last week in Atlanta, took the only break of his second set on the first point after a rain delay of more than an hour in the fourth game.
In the final set, Isner broke in the fifth game, fired four aces in a row in the final game and 10 aces overall in the last set.
"I've served incredibly well the last two weeks," Isner said. "That has carried me. I'm in a pretty good serving rhythm right now. I'm riding high with a lot of confidence.
"My body doesn't feel great, but nothing is wrong with me besides being a little tired and worn out," he said. "That's what happens when you're playing well. I'm a little beat up but I'll be ready to go."
Isner, ranked 20th, tops the season ATP rankings in aces with 587 in 37 matches and has a tournament-best 78 aces this week. But he is 0-3 all-time against Del Potro, having never taken a set.
Defending women's champion Magdalena Rybarikova, the seventh seed from Slovakia, beat Russian third seed Ekaterina Makarova 6-2 6-0 and will face either French fourth seed Alize Cornet or Germany's Andrea Petkovic in Sunday's final.
Del Potro, playing his first event since losing an epic Wimbledon semi-final to top-ranked Novak Djokovic, seeks his 15th career ATP crown and second of the year after Rotterdam in February. His most recent final was at Indian Wells, where he lost to Rafael Nadal.
Isner seeks his eighth career ATP title and third crown of the year, having also won in April at Houston.
