DOHA (Agencies) - Top-ranked Rafael Nadal overcame a second-set collapse to beat Lukas Lacko of Slovakia 7-6 (3), 0-6, 6-3 Wednesday and join Roger Federer in the quarterfinals of the Qatar Open. Earlier, Federer beat fellow Swiss Marco Chiudinelli 7-6 (5), 7-5. Nadal, who is also playing doubles with Marc Lopez, had a fever earlier this week and looked uncharacteristically slow and sluggish on court. In the second set, he won just five of 18 points on his serve-and 11 of 37 overall. It was only the 10th time in 575 career matches that Nadal lost a set 6-0, and the first since the decisive set of a final against Andy Murray at Rotterdam, Netherlands, in February 2009, when the Spaniard was bothered by a knee injury. Nadal picked up his game in the decisive set, breaking twice for a 3-0 lead after several unforced errors by Lacko. After dropping his serve once, Nadal broke again to clinch the match. Federer needed a strong baseline game to overcome Chiudinelli and stay in the hunt for a third tournament title in Doha. "It was an up and down match. I was a bit confused and lost focus (at the end of the first set), but I did well to concentrate better as the game went on."