Washington, 7 August 2011 | AP

Top-seeded Gael Monfils of France beat John Isner in three sets in a rain-delayed match on Saturday to advance to the final of the $US1.4 million ($A1.34 million) ATP Washington Classic.

Monfils will meet Radek Stepanek on Sunday after the Czech defeated American Donald Young 6-3 6-3.

Monfils, ranked seventh in the world, defeated Isner 6-4 3-6 7-6 (8-6).

“It was a bit tough in the head,” Monfils said.

Isner saved two match points in the 10th game of the deciding third set. On the second, Monfils felt Isner’s serve was wide, but the replay machine failed to operate and the call stood.

“I don’t think I played a bad tiebreaker,” Isner said. “I just cracked a little bit at 7-6.”

The start of the match was delayed almost two hours. There were two lengthy rain delays and the match finally ended at 1.15am local time.

The 32-year-old Stepanek convincingly beat 22-year-old Young.

In the seven years he’s been a professional, Young has been known as a promising player on the tour – and this week, the American won four straight matches for the first time in his career. Stepanek made sure there wasn’t a fifth.

“He’s a veteran – 10 years my senior,” Young said.

“I couldn’t get set into the way I wanted to play. It wasn’t that I was nervous, but more so he took me out of my game,” Young said.

Stepanek broke Young in the fifth and ninth games of the first set – and in the second game of the second set.

Stepanek won the second set’s first nine points and held service in the third game when he staved off Young’s only two break points of the match.

The left-hander entered this hardcourt tuneup for the US Open ranked 128th and with a 19-53 career record as a professional.

His run this week assures Young of returning to the top 100 in Monday’s ATP rankings. He still must qualify for the US Open’s main draw.

“I won four matches. I beat good players consistently for a week,” Young said.

After Stepanek won, he showed some emotion – punching the air and hitting a ball into the upper deck of the stadium.

The oldest player ranked in the top 100, Stepanek is seeking his fifth title – his first since winning two in 2009.