The second-seeded American, who tossed away another racket in anger in the second set, served 23 aces to beat the Spaniard.
Roddick will face unseeded German Bjorn Phau in the semifinals, with Dudi Sela of Israel playing Rainer Schuettler of Germany in the other.
In women's quarterfinal play, No. 2-seeded Ana Ivanovic was ousted by home favorite Zheng Jie 7-6 (4), 2-6, 6-4. A semifinalist at Wimbledon, Zheng overcame the French Open champion and former No. 1-ranked Serb, whose serves and ground strokes were erratic.
The match lasted almost three hours, filled with exciting rallies, service breaks, strings of deuce games and unforced errors.
In the three other quarterfinals, No. 1 Jelena Jankovic of Serbia beat Daniela Hantuchova of Slovakia 7-5, 6-1; No. 4 Svetlana Kuznetsova of Russia defeated Slovakian Dominika Cibulkova 6-2, 6-4 and Russian No. 5 Vera Zvonareva beat Anabel Medina Garrigues of Spain 6-0, 6-1.
In the semifinals, Zheng plays Kuznetsova and Zvonareva faces Jankovic.
Wimbledon semifinalist Zheng had noisy support from home fans at the Beijing Tennis Center. She is the only Chinese woman still playing in the tournament after four others lost in the first round. She also beat Ivanovic en route to the Wimbledon semifinals.
"This is a good win for me,'' she said. "It was in China and in front of my home crowd. There were lots of fans supporting me, which gave me even more motivation.''
Ranked No. 30 by the WTA, Zheng is hoping the ranking points earned in China will push her past her previous career high of No. 27.
Ivanovic has battled hand and leg injuries since winning in Paris, which has limited her play and confidence. However, she described her match Friday as "one of the best'' since the French Open.
"I haven't had many matches in the last three months,'' she said. "Since the French Open, you can count them on one hand the number of matches I played. I've been really struggling with injuries and it was a very frustrating time. But now I am confident again that I play 100 percent - and I can go on the court and work 100 percent.''
In the men's quarterfinals, Sela of Israel upset No. 6 Tommy Robredo of Spain 6-4, 6-1 to reach his first semifinal in a major ATP event. Sela was boosted by two wins over the weekend in a Davis Cup tie against Peru.
Sela trailed early against Robredo, but turned things around by attacking and hitting to the Spaniard's backhand.
"Every short ball he hit, I didn't wait,'' said Sela, who upset No. 1 David Ferrer on Thursday. "I went for the ball. I knew I had to attack him. If not he's going to move me around.''
Two other seeded players also lost on Friday.
No. 7 Schuettler ousted No. 4 Richard Gasquet 4-6, 6-3, 6-4. Phau defeated No. 3 seed and defending champion Fernando Gonzalez of Chile 6-3, 4-6, 6-3.
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