MASON, Ohio (AP) _ Andy Roddick built momentum for the U.S. Open by fighting off a stiff challenge from unseeded James Blake on Thursday night to advance to the quarterfinals of the Cincinnati Masters.

The two traded power serves and precise returns before the seventh-seeded Roddick wore down Blake for a 7-6 (2), 6-2 victory. Roddick has won all seven matches against Blake.

The emotion of the match was evident, with Blake crying out and Roddick throwing up his hands when their shots went astray. At one point when Blake trailed 4-2 in the second set and one of his returns was called out, he walked over to chair umpire Norm Chryst and asked about the call before returning to the court.

The crowd gave both players a standing ovation when the match ended and Roddick and Blake met at the net to shake hands.

Blake said he still thought his shot was in and suggested that tennis should use ``Spot Shot'' replay technology to trump possible human error.

``Humans are fallible,'' Blake said. ``Spot Shot's supposed to be accurate. Why not use it?''

Roddick dismissed Blake's complaint, saying the disputed shot was out.

Blake said that in the year since they last played, Roddick has learned to change speeds on his serves, alternating between 140 mph and 120 mph.

``He changes up on it a little,'' Blake said. ``It's a great weapon to have.''

Roddick, Guillermo Coria and Rainer Schuettler _ the only remaining seeded players of the tournament's original 16 _ all won Thursday to advance to the quarterfinals.

The sixth-seeded Coria needed just an hour and 15 minutes to beat Mikhail Youzhny 6-2, 6-1.

Schuettler, the No. 8 seed, outlasted Todd Martin 7-5, 3-6, 6-3. Martin hung on to push Schuettler despite having eight double-faults to Schuettler's three. Martin also had 32 unforced errors to his rival's eight.

Coria said he wasn't surprised by the elimination of so many seeded players.

``Today, tennis is really, really very competitive,'' the Argentine said through an interpreter. ``It's been happening the whole year, these upsets.''

The suburban Cincinnati tournament has not had an unseeded finalist since Chris Lewis in 1981. He lost in straight sets to John McEnroe, the No. 1 seed.

Blake had advanced to the round of 16 by beating 11th-seeded Sjeng Schalken 6-1, 6-4 in the second round Wednesday.

Roddick had advanced by defeating Ivan Ljubicic 6-1, 6-4. Roddick had 10 aces to three for Ljubicic.

In other matches Thursday, Mardy Fish defeated Arnaud Clement 6-2, 6-2; Robby Ginepri beat Gaston Gaudio 6-1, 7-6 (4); David Nalbandian topped Juan Ignacio Chela 6-4, 6-4, and Max Mirnyi eliminated Hicham Arazi 6-4, 6-7 (7), 6-4.

On Wednesday, 2002 Wimbledon runner-up David Nalbandian beat reigning Wimbledon champion Roger Federer 7-6 (4), 7-6 (5). Nalbandian has defeated Federer all four times they have played.

Carlos Moya, the defending champion of the Cincinnati Masters, was eliminated in the first round Monday by Fabrice Santoro.

Other seeded players who have been eliminated include Lleyton Hewitt, Sebastien Grosjean, Gustavo Kuerten, Paradorn Srichaphan, Jiri Novak and Tommy Robredo. Top-seeded Andre Agassi dropped out of the tournament last week, saying he needed a break before playing in this month's U.S. Open.