MADRID (AFP) - Rafael Nadal and Roger Federer rolled over outclassed opponents on Thursday as the top two seeds edged closer to a title showdown at the Madrid Masters. Nadal, aiming to lift his second trophy here following his 2005 triumph, stopped Richard Gasquet for the sixth time in as many meetings, his 6-4, 6-2 victory powering the top seed into the quarter-finals. Reaching the Sunday final will insure the Spaniard the world number 1 year-end ranking for 2008 after taking it from Federer in August. Federer faced Australian Open finalist Jo-Wilfried Tsonga for the first time and floored the Frenchman 6-4, 6-1. However, third seed Serbian Novak Djokovic was knocked out in straight sets by giant Croatian Ivo Karlovic 7-6 (7/4), 7-6 (7/5). "I've never played Jo before and that made it more difficult," said 13-time Grand Slam champion Federer "You don't know where he's going to serve, how he's going to play. I knew the danger and played carefully at the start. I'm happy with the score and glad to win in straight sets against a great player like Jo. "I was able to land the KO punch like in a heavyweight boxing match. I got the first one in and that was good for me." Federer will play for the semi-finals against Argentine Juan Del Potro, who knocked out defending champion and Davis Cup teammate David Nalbandian 6-4, 6-2.Karlovic hammered 21 aces and won 89 percent of first-serve points in his upset win over world number three Djokovic who failed to convert three break point chances in the match. In addition to his overwhelming serve Karlovic was often brilliant at net and on match point, with Djokovic serving, he charged the net after a brief baseline exchange and forced a forehand error.Karlovic will face France's Gilles Simon for a place in the last four.Nadal required less than 90 minutes to advance, leaving his French opponent Gasquet to pick up the pieces after winning just three career sets against the reigning Roland Garros, Wimbledon and Olympic champion. "Richard made a lot of mistakes with his backhand, which is usually his best shot," said Nadal. "He's had an inconsistent year, but in 2007 he was in the Top ten. He is always dangerous." Nadal looked in devastating touch in his campaign to lift a ninth title this season but will face Lopez, the 40th-ranked Spaniard, who is in impressive form having knocked out Swiss tenth seed Stanislas Wawrinka 6-4, 6-4. "It's going to be difficult to win, let's see if I am okay with my serve so that I can play more comfortably. That will be very important in order to win the match," said Nadal. Andy Murray was hoping that a jolt to his chronically weak knee would not prevent him from continuing this week after defeating Marin Cilic 7-5, 7-6 (7/2). The Scottish fourth seed advanced after reversing an early break when trailing 3-5 in the first set against the Croatian. Murray said he will hope to make his Friday match against Gael Monfils, who defeated Andy Roddick 6-4, 3-6, 6-3. "As long as the pain is bearable, I'm ready to play," said the US Open finalist.