KEY BISCAYNE, Fla. -- Andre Agassi's absence from the Australian Open this year helped Thomas Johansson win his first Grand Slam title. Johansson wasn't so lucky at the Nasdaq-100 Open.

The ninth-seeded Agassi, seeking his fifth Key Biscayne title and second in a row, beat the eighth-seeded Johansson 7-5, 6-2 Tuesday to reach the quarterfinals.

A wrist injury kept Agassi from bidding for his third consecutive Australian Open championship in January. He's 12-2 since returning and looked sharp against Johansson.

"It was definitely a letdown not playing Australia this year," Agassi said. "It's been a great place for me to get my year started. But now I've got a lot of energy, and I'm coming out of my shoes looking for competition."

Agassi's opponent Wednesday will be No. 20 Nicolas Lapentti, who beat Adrian Voinea 6-2, 3-6, 6-3.

Two men's fourth-round matches ended with injuries on a sunny, humid, 85-degree afternoon. No. 5 Tim Henman retired because of a stiff neck, trailing No. 12 Roger Federer 6-2. Gaston Gaudio quit with severe cramping, trailing Juan Ignacio Chela 6-1, 5-7, 4-3.

Henman hurt his neck when he collided with a stranger going through a doorway Monday.

"I can't really look up," Henman said. "So that rules out serving."

Chela's quarterfinal opponent will be 1998 champion Marcelo Rios, who beat No. 16 Alex Corretja 6-2, 6-2.

Top-seeded Lleyton Hewitt needed only 10 minutes Wednesday to complete his rain-interrupted victory, beating American James Blake 6-4, 6-1.

Hewitt led 3-1 in the second set Tuesday when the match was suspended. He broke Blake's serve six times, including twice Wednesday to complete the fourth-round victory.

Hewitt, seeking his third title this month, extended his winning streak to 14 matches. He earlier won at Scottsdale and Indian Wells, and has won 21 consecutive matches on U.S. hardcourts dating back to his title run at the U.S. Open last year.

The weather was sweltering when Agassi and Johansson took the court. Agassi, progressively more confident in his groundstrokes, broke serve for a 6-5 lead and served out the set.

In the opening game of the second set, Agassi came up with the shot of the match to break again. He chased down a Johansson volley to angle a running forehand crosscourt for a winner.

"That was a beauty," Agassi acknowledged. "Sometimes those shots happen."

Agassi controlled the baseline rallies by keeping Johansson off balance and showed unusual snap with his serve, belting eight aces, including one at 120 mph.

"You go out there with a healthy respect for somebody that's won the first slam of the year," Agassi said. "It's an opportunity to raise your game."

Agassi is playing for the 16th consecutive year at Key Biscayne, where he won titles in 1990, 1995, 1996 and 2001.

Henman will not risk flying home to Britain until he has had treatment on his neck.

"I don't think flying would do me much good," he said.

"I think there's so much sort of spasm around my neck and my back, I just need to let that settle down.

"Because I'm going to be here in Miami I might as well take advantage of the (medical) facilities."

Henman's next tournament is the Monte Carlo Masters starting on April 15, allowing him plenty of rest.

"Hopefully I'll be able to get it sorted out in due course," he said.

Information from Reuters was used in this report.