BRISBANE (Agencies) - Defending champion Andy Roddick advanced to the quarterfinals of the Brisbane International on Wednesday, serving 15 aces to beat Alexandr Dolgopolov of Ukraine 6-4, 6-1. The second-seeded Roddick controlled the match with his powerful serve, landing 71 percent of his first serves and winning 87 percent of those points. His barrage of aces helped victims of devastating flooding in Australia's Queensland and New South Wales states after he pledged to donate $100 for every ace he serves at the Brisbane tournament. Sam Stosur of Australia, the top-seeded women's player, made the same pledge but was eliminated in the second round. "A lot of the credit should go to Sam Stosur," Roddick said. "It was her initiative. She came up with the idea and I was happy to follow her lead." Roddick dropped his serve early in the first set at Pat Rafter Arena, but gradually started to dominate the hard-hitting Dolgopolov. "I knew that he was aggressive to the point of psychosis," Roddick said. "He came out in the first six games and I didn't really do much wrong. ... When someone is going to try and hit a winner from whatever ball they get on the very first shot, and if they convert, there's very little you can do. "It was my plan to make him come up with those shots for the better part of a couple of hours and it caught up to him a little bit. And when it caught up to him it got away from him pretty quickly." Roddick will next face fifth-seeded Marcos Baghdatis in the quarterfinals. The Cypriot beat Lukasz Kubot of Poland 6-2, 6-2. "It's nice to play guys like Andy, top-10 players," Baghdatis said. "It's a test match before the Australian Open and it will be a great match." Also, 2010 runner-up Radek Stepanek of the Czech Republic beat fourth-seeded American Mardy Fish 6-2, 6-1. In the women's tournament, crowd favourite Jelena Dokic of Australia dropped 10 straight games in a 6-0, 6-1 loss to Andrea Petkovic of Germany, a setback ahead of the Australian Open. Dokic said she has a stomach virus and had "nothing to give" in the match.