KEY BISCAYNE, Fla. (AP) – Roger Federer blew a lead, missed easy volleys, clanked forehands off his frame and still managed to win.

The world No. 1 survived a scare Monday night and beat Mariano Zabaleta 6-2, 5-7, 6-3 in the third round of the Nasdaq-100 Open.

Federer extended his winning streak to 18 matches and improved to 44-1 since the start of last year’s U.S. Open. But he hardly looked invincible against the unseeded Zabaleta.

Serving for the match at 5-3 in the second set, Federer double-faulted on break point, then lost his next service game as well. After some shaky moments, he broke Zabaleta for a 5-3 lead in the final set, then served out the match.

“You start to think about everything,” Federer said. “He’s getting more pumped. The rallies are going his way. You’re forcing some issues. To be on top in the end, I’m really, really satisfied.”

When Zabaleta put a tough volley into the net to end a furious rally on match point, Federer smacked a ball out of the stadium in relief.

He won despite 42 unforced errors.

“Today wasn’t great always, but I came through,” Federer said.

Joining him in the fourth round was Taylor Dent, who beat a top-10 player for the fourth time this year by eliminating Guillermo Coria 6-3, 6-4. Dent dominated with his big serve, but he also chased down a drop shot by the crafty Coria and angled his reply crosscourt for a winner.

“It’s always nice to beat the South Americans and Spaniards at their own little game,” Dent said with a smile.

The departure of Coria, the runner-up last year, left just one of the six highest-ranked players – Federer – in contention with four rounds still to go. The highest-seeded man left in one half of the draw is No. 13 Ivan Ljubicic.

Dent, seeded 31st, used his serve-and-volley game to keep Coria on the defensive.

Dent lost only four points on his first serve, never faced a break point and won 37 points at the net.

He used his wheels, too. Pudgy and injury-prone in the past, Dent said sprint work has reduced his weight at least 15 pounds from a high of 215.

“He certainly has a game that should cause problems for a lot of people,” said Andre Agassi, who also won and might face Dent in the quarterfinals. “I would expect him to have these wins a lot more often.”

Six-time champion Agassi hit 12 aces and took barely an hour to beat Arnaud Clement 6-2, 6-4.

On the women’s side, Belgians Justine Henin-Hardenne and Kim Clijsters continued their comebacks from injury.

Henin-Hardenne, seeded 19th and playing in her first tournament since the U.S. Open, reached the quarterfinals by beating No. 7 Alicia Molik 6-4, 2-6, 6-2. The three-time Grand Slam champion had been sidelined by a virus and knee injury.

“What I’m doing here this week is very good,” Henin-Hardenne said. “I found my game again.”

Clijsters, unseeded and coming back from wrist surgery, beat No. 5 Anastasia Myskina 6-3, 6-4. Clijsters has won 11 consecutive matches, including her first tournament title in 13 months earlier this month at Indian Wells.

“I definitely didn’t expect to be playing so many matches on this trip” to the United States, Clijsters said. “So everything is a bonus.”

Joining French Open champion Myskina on the sideline was another Russian, Svetlana Kuznetsova, the U.S. Open champion. She lost to 17-year-old Ana Ivanovic of Serbia-Montenegro 6-3, 3-6, 7-5.

“This is quite a big result for me,” said Ivanovic, who won her first WTA Tour title in January in Canberra, Australia. “I think I’m pretty happy.”

The 6-foot Ivanovic next plays top-seeded Amelie Mauresmo, who beat No. 16 Karolina Sprem 6-1, 7-5. No. 2 Maria Sharapova eliminated No. 23 Shinobu Asagoe 6-1, 6-2 and will play Henin-Hardenne next.

No. 4 Elena Dementieva overcame nine double faults to rally past 17-year-old Tatiana Golovin 3-6, 6-2, 6-1.

While Coria was eliminated, fellow Argentine Gaston Gaudio advanced and will play Agassi next. The No. 7-seeded Gaudio beat No. 27 Sebastien Grosjean 6-2, 6-3.

No. 6 Tim Henman swept another Argentine, No. 28 Juan Ignacio Chela, 6-3, 6-1.

AP-ES-03-28-05 2201EST