NEW YORK (AFP) - Five-time defending champion Roger Federer booked a third-round US Open date with former world number one Lleyton Hewitt Wednesday while six-time Grand Slam winner Rafael Nadal cruised in his opener. World number one Federer, seeking his 16th career Grand Slam title, ousted Germany's Simon Greul 6-3, 7-5, 7-5 while Nadal's bid to complete a career Slam began with a 6-2, 6-2, 6-3 victory over Frenchman Richard Gasquet. Knee tendinitis kept Nadal from defending his 2008 Wimbledon title and sidelined him for two months, making this his first Grand Slam match since losing to Sweden's Robin Soderling in the fourth round of the French Open, a defeat that snapped his four-year title streak at Roland Garros. "Seems like I was two years outside of competition. I was two months," Nadal said. "I'm fresher than ever in this tournament. I don't know if this fresher is good but I'm fresh." That's dangerous news for Federer, who has lost to Nadal in five Slam finals and could meet him again for this year's US Open crown. "Fantastic having him back. It seems like he is doing well. He won very easily and that's great," Federer said. "If he's physically in great shape, obviously he's got a great chance to go far."If he's on, he's going to be hard to stop." Greul provided a somewhat grueling test for Federer, who was forced to save two set points in the 10th game before the Swiss star held, broke in the 11th game and held again for the set. Federer netted a backhand to surrender a break in the second game of the second set and trailed 0-30 in the fourth game before roaring back, taking six of the last seven games to move on after one hour and 58 minutes. "I knew I could be in for a battle," Federer said. "The level was really high. There was a lot of intensity. I'm glad to get through with a win." Federer's US Open unbeaten streak stretched to 37 matches as he set up a rematch of his first US Open final triumph in 2004 against Australia's Hewitt, who defeated Argentina's Juan Ignacio Chela 6-3, 6-3, 6-4. "I started his run here in the finals in 2004," Hewitt said. "It would be nice if I could be able to be the one to finish it." Federer has beaten the Aussie 13 times in a row and stretching that streak would ensure the Swiss star remains atop the rankings no matter what else happens in the Flushing Meadows fortnight. "You've got to respect the player he is," Federer said. "If things go badly you can lose very quickly." Nadal fired seven aces and made only 10 unforced errors to win in one hour, 41 minutes, improving the third-seeded Spaniard to 7-0 lifetime against Gasquet and booking a second-round date against Germany's 129th-ranked Nicolas Kiefer. "It felt good," Nadal said. "I served well in the important moments. I played very well on my backhand, which is very important in my game. I'm very happy to be in the second round." Nadal can complete a career Grand Slam by capturing his first Flushing Meadows crown. "I hope I have the last Slam title here," he said. "They say the last is the most special." Nadal, who joked that his new haircut "makes him feel younger", shrugged off any notion of lingering knee trouble."I don't have pain so I don't think (about it)," Nadal said. "I'm playing and practicing with a good attitude. That's the important thing right now, trying to get into a good rhythm for the matches." Argentine sixth seed Juan Martin Del Potro advanced with a 6-3, 6-3, 6-1 victory over countryman Juan Monaco. The 20-year-old French Open semi-finalist will next face Austrian Jurgen Melzer. Former world number one Marat Safin concluded his Grand Slam career with a 1-6, 6-4, 6-3, 6-4 first-round loss to Melzer. The 29-year-old Russian, a two-time Grand Slam winner, will retire at year's end.Safin, who won the 2000 US Open and 2005 Australian Open, might play again this year, he is happy the Slam farewell tour has finally run its course.Spain's Juan Carlos Ferrero ousted France's Fabrice Santoro 6-4, 6-3, 6-3. It was a men's record 69th career Slam appearance and 45th in a row for Santoro, who will retire at the end of the season. Frenchmen Gilles Simon and Gael Monfils, the ninth and 13th seeds respectively, also advanced. Monfils beat countryman Jeremy Chardy 6-1, 6-4, 6-3. Simon downed Spain's Daniel Gimeno-Traver 6-4, 7-6 (7/3), 6-3.