Roddick managed only one break and had to fight off five break points to advance to a quarter-final clash with German veteran Tommy Haas.

Second-seeded Argentinian Juan Martin del Potro and third-seeded American James Blake also advanced.

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Del Potro, ranked seventh in the world, vanquished Japanese teenager Kei Nishikori 6-2, 6-2.

Del Potro is trying to build on early season success. He opened 2009 by winning his fifth career ATP Tour title in Auckland and followed with a quarter-final run at the Australian Open.

Del Potro had little trouble against Nishikori, delivering eight aces, saving five of six break points and capturing five breaks in the match as he advanced to a meeting with fifth-seeded American Mardy Fish.

Fish advanced with a 6-2, 6-7 (4/7), 7-5 win over compatriot John Isner.

Blake dispatched France's Florent Serra 6-4, 6-3 in just 67 minutes.

Blake booked a quarter-final date with sixth-seeded countryman Sam Querrey, a 6-3, 6-2 winner over Germany's Denis Gremelmayr.

Blake was dominant against Serra, notching 13 aces, saving five break points and capitalizing on two of three break chances.

Querrey finished Gremelmayr in swift fashion, posting all 12 aces in the match. He broke his opponent three times and never dropped his own serve.

In the day's other singles match, qualifier Todd Widom took three sets to oust Taylor Dent, 6-7 (5/7), 6-3, 6-2.