Del Potro advances to D.C. quarters, extends winning streak to 16

John Isner, last year's Legg Mason runner-up, will face Del Potro in the quarterfinals after beating Donald Young 6-4, 7-6 (4).

"Obviously, the guy has as much confidence as anybody playing tennis today," Isner said. "I'll have to do everything I can to disrupt his flow."

Isner was able to throw off Young's flow with 17 aces in the match, and Young was visibly frustrated at the end of the tiebreaker. After hitting a long unforced error to go down 5-4 in the tiebreaker, Young threw his racket to the ground. After failing to return Isner's next serve, Young kicked the racket before going to his bag for a new one.

The new racket didn't help Young, who returned Isner's final serve wide to send Isner to the next round.

The two-set victory in Washington was a new experience for Isner. In his first Legg Mason appearance last year, Isner won five matches in third-set tiebreakers before losing to top-seeded Andy Roddick in the final. He again went to the third-set tiebreaker in his opening-round match against No. 8 seed Marcel Granollers-Pujol.

Haas will face Alejandro Falla in the quarterfinals. Falla prevailed in two tiebreakers against Florent Serra, winning 7-6 (2), 7-6 (11).

Falla, who defeated fifth-seeded Mardy Fish in the first round, said his right quad was cramping when he was down 6-5 with Serra serving in the second set. He battled through it to force the tiebreaker and throughout the 24-point final game.

"Everything happened in the tiebreak," Falla said. "Set point for him, match point for me. It went so long -- there were long rallies and some amazing balls."