Federer advances after opponent taken ill

MIAMI (Reuters) - World number one Roger Federer advanced to the fourth round of the Sony Ericsson Open on Monday when his Swedish opponent Robin Soderling retired from their third-round match because of illness.

The Swiss top seed, who won the title in 2005 and 2006, was leading 6-4 3-0.

"I think it was good for me to go out there and play today," Federer told reporters. "Apparently it was a fever. There was no point in his continuing and risking his health,"

"I hope I can make it step by step and once you make it to the quarter-finals or semi-finals you start thinking about winning the title."

One day after upsetting world number two Ana Ivanovic in the third round, Lindsay Davenport was beaten 6-3 6-4 by 13th seed Dinara Safina in the women's singles.

Davenport, who had won both of their previous matches, broke serve in the opening game of the match, but then lost her serve in the second and eighth games of the first set.

Davenport broke serve first in the second set as well, this time in the second game, but lost her serve in the fifth and ninth games.

"This is the first match that I just really felt like I couldn't figure out a way to kind of get back into it," said Davenport, who has won four titles since returning to the tour after giving birth to her first child last June.

"It was obviously windy today and hasn't been windy the rest of the tournament. I was just kind of fighting the wind, trying to find my shots."

Top-seeded Justine Henin, hoping to claim her first title in Miami, expended little energy winning her fourth-round match against Elena Venina of Russia 6-2 6-2.

Reversing the result of their fourth-round match in Miami last year, third-seeded Svetlana Kuznetsova recorded a 7-6 6-3 victory over 16th-seeded Shahar Peer of Israel.

Sixth-seeded Venus Williams defeated Danish teenager Caroline Wozniacki 6-3 6-3 to advance to the quarter-finals.

Williams said she believed her game was good enough to claim a fourth career Sony Ericsson Open title after winning in Miami in 1998, 1999 and 2001.

"I'm always trying to take it to another level, regardless," Williams said. "If I'm playing on cloud nine, I'm trying to get to cloud 10 and actually cloud 11."

(Editing by John Mehaffey)