HANOVER, Germany -- Pete Sampras is playing too well to have to worry about the details of a tournament that could give him a place in tennis history.
After beating Carlos Moya 6-3, 6-3 on Wednesday, Sampras said he was unaware that he had clinched a place in the semifinals of the ATP World Championship.
"That's nice to hear," Sampras said after being told he had reached the final four. "It's certainly a good feeling to be here over the weekend."
Not feeling so good was Andre Agassi, who withdrew from the tournament because of a back injury.
Agassi quit in the third set of his match against Alex Corretja on Wednesday. He will be replaced in the round-robin draw by Britain's Greg Rusedski.
Sampras is seeking to become the first man to finish No. 1 in the world for six years in a row. He shares the record with Jimmy Connors.
Marcelo Rios, the only player who can threaten Sampras, trails by 33 points in the computer rankings and has to do better than Sampras in the season-ending championship that brings together the top eight players of the year.
But Rios, who was not scheduled to play Wednesday, lost his first match to Tim Henman and is battling a back injury. He now has to win his next two round-robin matches to reach the semifinals and stay in the chase.
The eight players are split into two groups and Sampras and Rios cannot meet until the semifinals.
"It helps," Sampras said of Rios losing the first match. "I'm also helping myself by winning. I can't really be too concerned about what Marcelo is doing.
"I have to concentrate on my matches. If I take care of things myself and go out and win, then it should be hopefully good enough. But I must admit I was rooting for the Englishman (Henman) yesterday."
Sampras was certainly good enough to beat Moya in only 62 minutes, with the help of 13 aces. Moya, the French Open champion who is now 1-1, had beaten Sampras in a group match last year but Sampras went on to win the $3.5 million event for the fourth time.
On Tuesday, Sampras was equally impressive in beating Yevgeny Kafelnikov in straight sets.
"It's not easy to play well like I have been today and yesterday. I was coming into today's match pretty confident," Sampras said. "I wanted to make sure I was coming in a little bit more than last year, chipping and charging, trying to put as much pressure on him as possible.
"Last year, I must admit, I felt a little flat. This year, with the ranking up for grabs, I just made a concerted effort to come here a little bit early and prepare as best as I can.
While Sampras moved on, Agassi moved out. He quit his opening match against Corretja with the Spaniard leading 5-7, 6-3, 2-1.
Agassi was practicing with Corretja on Monday when he fell and hurt his back, and had been receiving shots and other treatment since then.
"It was definitely painful even this morning in my warmup. I needed to give it a go, at least try to keep the points short," Agassi said. "But I hit a swinging volley and when I twisted it was just like somebody stuck a knife in me. Pretty soon it got quite pointless."
Rusedski will play Rios on Thursday. Corretja plays Henman and Sampras meets Karol Kucera.
Kafelnikov beat Kucera 6-7 (3-7), 6-3, 6-2 in the last match Wednesday and improved to 1-1. Kucera dropped to 0-2.
Agassi, who won the event in 1990, surged back No. 4 this year after falling as low as No. 141 at the same time last year. But he has not done well at major tournaments this season.
"The year has been great for me in many respects, but the great tournaments have been pretty disappointing," Agassi said. "I've worked really hard and had to grind week after week to get myself in position, only to struggle when I got into position."