Melbourne, January 18:

Maria Sharapova was struggling. But last year’s runnerup at the Australian Open was through to the fourth round with a 6-3, 6-0 victory over Elena Vesnina that was a lot harder than the score indicated.

Defending champion Serena Williams and top-ranked Justine Henin also advanced against opponents with similar games. Williams next faces 12th-seeded Nicole Vaidisova, while Henin puts her 31-match winning streak on the line against Taiwan’s Hsieh Su-Wei.

But 2006 champion Amelie Mauresmo, seeded 18th, fell 3-6, 6-4, 6-4 to Australia’s Casey Dellaqua, who had a year-end No 78 ranking and had earlier ousted No 15 Patty Schnyder.

Former No 1 Mauresmo double-faulted while serving at 4-5, deuce in the third set. Dellaqua then finished it off with a forehand inches inside the corner that Mauresmo let drop for a winner as the Rod Laver Arena crowd erupted in cheers for the last local hope in the women’s draw. Dellaqua earned a matchup against No 3 Jelena Jankovic, a 6-2, 4-6, 6-1 winner over No 30 Virginie Razzano of France.

On the men’s side, second-ranked Rafael Nadal and No 4 Nikolai Davydenko advanced in straight sets but American sixth-ranked Andy Roddick was ousted by Germany’s Philipp Kohlschreiber 6-4, 3-6, 7-6 (9), 6-7 (3), 8-6.

Nadal next plays No 23 Paul-Henri Matthieu, who had a five-set victory over Stefan Koubek, while Daveydenko meets fellow Russian Mikhail Youzhny, who downed No 20 Ivo Karlovic. Eighth-seeded Richard Gasquet also advanced and next faces unseeded Jo-Wilfried Tsonga.

After routing Lindsay Davenport in the last round, Sharapova seemed puzzled and frustrated that she couldn’t put away Vesnina until she finally put it all together and ran off the last nine games. Sharapova next faces another Russian, No 11 Elena Dementieva, who beat Israel’s Shahar Peer.

Williams improved her record to 26-1 at Melbourne Park since the start of 2003. With opponent Victoria Azarenka liking a fast pace, there were no high, looping moon balls here, just power tennis. Her serve was working particularly well, with 15 aces and a stretch of seven service games in which she yielded only six points.

Henin, the 2004 champion, improved her record here to 15-1 since 2004 with a 7-5, 6-4 win over Schiavone. She and Schiavone kept each other on the run constantly, mixing up speed and spins to keep each other off-balance.