Top seed Andy Roddick ended his losing streak against fellow American James Blake at the ATP Morgan Keegan Championships but third seed Radek Stepanek and fourth seed Tommy Haas crashed out in Memphis on Wednesday.
Roddick, who headed into his first-round clash having lost his last three matches against Blake, had a wobble in the second set but eventually prevailed 6-3 4-6 7-6 (7-3).
Belgium’s Xavier Malisse accounted for Haas, booking his place in round two with a 6-4 3-6 6-4 victory over the German.
In other first-round action on Wednesday, Leonardo Mayer of Argentina beat American Mardy Fish 6-4 6-0 while eighth seed Sam Querrey breezed through his all-American clash with Rajeev Ram 6-2 6-3.
In the second round, Latvian youngster Ernests Gulbis stunned Stepanek, knocking out the Czech player 7-6 (7/5) 7-5.
American sixth seed John Isner also advanced to the quarter-finals with a 6-7 (3/7) 6-4 6-4 victory over Finland’s Jarkko Nieminen while Germany’s Philipp Petzschner ousted Kazakhstan’s Evgeny Korolev 7-6 (7/5) 7-6 (7/5).
In the WTA Cellular South Cup, top seed Maria Sharapova cruised past American Bethanie Mattek Sands 6-1 6-1 in the second round to set up a last-eight meeting with eighth seed Elena Baltacha.
The British number one earlier continued her fine form with a 6-4 6-4 win over Canadian qualifier Valerie Tetreault.
Baltacha became the second Briton in the quarter-finals, with Anne Keothavong having already ousted Portuguese teenager Michelle Larcher De Brito 6-3 6-1 to secure a date with Karolina Sprem. Sprem got the better of fellow Croatian Ajla Tomljanovic 3-6 6-2 6-0.
Second seed Melanie Oudin encountered few difficulties in seeing off fellow American Lilia Osterloh 6-2 6-1 to also progress. She will next play Sweden’s Sofia Arvidsson, who defeated seventh-seeded American Vania King 3-6 6-4 6-2.
Third seed Kaia Kanepi of Estonia will face fifth-seeded Czech Petra Kvitova in the quarter-finals after both advanced from the second round on Wednesday.
Kanepi battled from a set down to overcome Czech Nicole Vaidisova 4-6 6-1 6-3 while Kvitova enjoyed a more straightforward 6-4 7-5 triumph over Holland’s Michaella Krajicek.