Andy Roddick serves past Taiwan's Yen-Hsun in Memphis

Defending champion Andy Roddick was pushed for the second straight day before prevailing over Lu Yen-Hsun 7-6 6-4 on Thursday during the second round of the Memphis Championships.

After a tough three-set victory over fellow American James Blake in the opening round, Roddick relied on his serve to turn back Taiwan''s Lu, who saved seven break points but faltered in the second set at 4-4. 

Roddick, bidding for his third Memphis title, did not concede a single break and clubbed 10 aces. He next faces fellow American Sam Querrey, who defeated Argentina's Leonardo Mayer 6-4 6-0. 

In the women's draw, second-seeded American Melanie Oudin crashed out, losing to unranked Swede Sofia Arvidsson 6-1 6-3.       

Top seed Maria Sharapova of Russia plays eighth seed Elena Baltacha of Britain in a late match.