Juan Martín Del Potro and Rafael Nadal progress at Australian Open

Juan Martín Del Potro survived a lapse of concentration in the second set to reach the fourth round of the Australian Open. The US Open champion beat Germany's Florian Mayer in four sets - 6-3, 0-6, 6-4, 7-5 - in two and a half hours. Del Potro was keen to avoid another five-setter after going the distance against James Blake in the second round. And he regained his composure in the third set, serving solidly, and seemed untroubled by his injured wrist. The world No5 will play Marin Cilic or Stanislas Wawrinka on Sunday for a place in the quarter-finals. Rafael Nadal was made to work for his win against Philipp Kohlschreiber but eventually beat the German No27 seed 6-4, 6-2, 2-6, 7-5. Nadal had beaten Kohlschreiber five times before today's match with three of those wins coming in straight sets. However, those games were all on clay and Kohlschreiber has always made a match of it on hard court. Andy Roddick has also reached the fourth round after a 6-7, 6-4, 6-4, 7-6 win over Spain's Feliciano López , an opponent he has never lost against. The American will next face Chile's Fernando González after the 11th seed defeated Kazakhstan's Evgeny Korolev in five sets. "He [González] is a very dangerous player," Roddick told Reuters. "Some days he comes out, looks like he's playing ping pong the way he can sling the ball around. I think I'm going to have to keep serving the way that I have been, kind of try to control the pace of the match with my first serve. We'll see."