MELBOURNE, Australia — U.S. Open champion Juan Martin del Potro held off James Blake in a marathon five-setter today, while Justine Henin advanced in her Grand Slam comeback with a 7-5, 7-6 (6) win over the reigning Olympic champion.

Fourth-seeded del Potro beat his 30-year-old American rival 6-4, 6-7 (3), 5-7, 6-3, 10-8 in 4 hours, 17 minutes on Hisense Arena, the second showcourt at Melbourne Park.

Seven-time Grand Slam singles champion Henin, meanwhile, produced the biggest win of her comeback from 20 months in retirement with a 7-5, 7-6 (6) defeat of fifth-seeded Elena Dementieva in the night match on Rod Laver Arena, the center court.

The win for the unranked Henin was another step closer to a possible quarterfinal match against U.S. Open champion Kim Clijsters, who scored a 6-3, 6-3 win over Tamarine Tanasugarn of Thailand.

It was Clijsters' U.S. Open title only three tournaments back from two years in retirement that inspired Henin, her fellow Belgian, to return to the tour.

Earlier today, Rafael Nadal and Andy Roddick continued their paths toward a possible semifinal matchup.

But the thread that ties Nadal and Roddick together from 2009 — Roger Federer, who beat Roddick in the semis last year before losing to Nadal in the final — likely will still have something to say about who the eventual champion is Jan. 31. The top-seeded Swiss star is on the other side of the draw and couldn't meet either Nadal or Roddick until the final.

Nadal breezed to a 6-2, 6-2, 6-2 second-round win over Lukas Lacko of Slovakia while Roddick was equally untroubled by his opponent in a 6-3, 6-4, 6-4 win over Brazil's Thomaz Bellucci.

Britain's Andy Murray, who could meet Nadal in the quarterfinals, advanced to the third round after beating Marc Gicquel of France 6-1, 6-4, 6-3. Murray is attempting to win his first Grand Slam title and become the first British man in more than 70 years to win a singles major.

Del Potro, who beat Federer in last year's U.S. Open final, had a chance to serve for the match at 6-5 in the fifth after breaking Blake. However, Blake broke back immediately, helped by two errors from the 21-year-old Argentine.

Del Potro again broke Blake for a 9-8 lead and another chance to serve it out. He closed with a big serve out to Blake's backhand side on his first match point. Blake fell to 4-13 in five-set matches.