MELBOURNE, Australia - Rafael Nadal and Roger Federer are taking similar paths to a potential semifinal matchup at the Australian Open.

Meanwhile, the last U.S. man fell out of the tournament when No. 16 John Isner lost to Spaniard Feliciano Lopez 6-3, 6-7 (3), 6-4, 6-7 (0), 6-1. It marks the first time since the start of the Open Era in 1968 that no American men have reached the fourth round at the Australian Open

Neither the four-time Australian champion Federer nor 2009 titleholder Nadal have dropped a set, although Federer's path was made easier by a walkover win in the second round. They are in the same half of a Grand Slam singles draw for the first time since 2005.

The longtime rivals played back-to-back matches at Rod Laver Arena on Friday. Nadal, his right knee still taped from a recent injury, showed no problems while moving briskly around the court in a 6-2, 6-4, 6-2 win over qualifier Lukas Lacko.

Federer then edged Ivo Karlovic 7-6 (6), 7-5, 6-3, saving a set point in the tiebreaker with a scrambling lob over the 6-foot-10 Croatian. Nadal will face Lopez, and Federer will play Australian teenager Bernard Tomic on Sunday.

"He gave me a second serve and gave me a slight chance," Federer said. "Might have had a little bit of a lucky volley."

Karlovic agreed.

"It was unlucky ... one in a 100 that I'm going to lose that point," Karlovic said. "I didn't really expect him to do that. I was there, I just miscalculated how much I was jumping. If I would have won that, everything would be different, but that's life."

Nadal had few dramas in his match against Lacko. Over the weekend, he felt a sharp pain in his knee while sitting in his chair in his hotel. He initially feared it would cause him to withdraw from the tournament.

Three matches later, Nadal says "the knee is fine ... being in the fourth round without losing a set, it's fantastic news."

Isner was disappointed with the outcome of his match. The last American to win the Australian Open was Andre Agassi in 2003, his third win in four years at Melbourne Park.

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"It's very ugly, to be honest, to have no one in the round of 16 ... very disappointing, not a good effort from the Americans," Isner said. "We've got to try to rectify that next time the big tournaments roll around."

No. 7 Tomas Berdych beat No. 30 Kevin Anderson of South Africa 7-6 (5), 7-6 (1), 6-1 and will play No. 10 Nicolas Almagro of Spain, who beat 21st-seeded Stanislas Wawrinka of Switzerland 7-6 (2), 6-2, 6-4.

Philipp Kohlschreiber of Germany defeated Alejandro Falla of Colombia 6-3, 6-2, 7-6 (3), 11th-seeded Juan Martin del Potro beat Yen-Hsun Lu of Taiwan 6-2, 6-3, 6-0 and Tomic defeated 13th-seeded Alexandr Dolgopolov of Ukraine 4-6, 7-6 (0), 7-6 (6), 2-6, 6-3. Del Potro plays Kohlschreiber in the fourth round.

Defending champion Novak Djokovic and fourth-seeded Andy Murray, who has lost in the final at Melbourne Park the last two years, play their third-round matches Saturday, with a Djokovic-Murray replay possible in the semifinal.