Andy Roddick defeats Rajeev Ram in Atlanta

Top-seeded Andy Roddick weathered high temperatures to beat Rajeev Ram 6-1, 6-7 (1-7), 6-3 in the second round of the Atlanta Tennis Championships.

Roddick, who will face seventh-seed Xavier Malisse of Belgium in the quarter-finals, is aiming for his 20th career tournament title on hardcourts and third this year.

Malisse defeated Ukraine's Illya Marchenko 6-3, 6-3, while third-seeded Lleyton Hewitt lost a late match 6-4, 6-2 to Slovakia's Lukas Lacko.

"The first game of the third, I was down a couple of break points," Roddick said. "If he breaks the first game of the third, I think it's a long way back because he started serving a little bit better in the second set. That was probably the pivotal moment in the match."

Former top-ranked Hewitt blamed an injury, which he refused to disclose, for keeping him from playing at full capacity.

He acknowledged, however, that the injury occurred before he arrived in Atlanta.

Lacko now goes on to play South Africa's Kevin Anderson, a 7-5, 6-3 second-round winner over Donald Young.