His game still nowhere near where he wants it to be, Pete Sampras struggled into the semifinals of the ATP Tour World Championship today by beating Nicolas Lapentti, 7-6 (7-2), 7-6 (7-5).

"He really made me work hard," said Sampras, who has dropped to No. 5 in the rankings.

Sampras actually needed to win only one set to advance, and he admitted he didn't know that was all that was required of him in the tournament's complicated tiebreaking mechanism.

"I didn't play great, but I got through," he said. "That's the bottom line."

Coming off a three-month layoff because of hip and back injuries, Sampras joins Andre Agassi, Yevgeny Kafelnikov and Nicolas Kiefer in the semifinals of the $3.6 million season-ending tournament.

Kiefer, inspired by a boisterous, hometown crowd, hit booming winners from all corners of the court in beating Kafelnikov, 6-1, 4-6, 6-2.

"It's a great experience I am having at the moment, 14,000 spectators behind me and cheering the whole time," Kiefer said.

Although Kiefer upset Kafelnikov, both moved on. Agassi was idle today and already had qualified in this round-robin event.

In the semifinals, it's Agassi vs. Kafelnikov and Sampras vs. Kiefer.

Kafelnikov, ranked No. 2, was assured of advancing before he played Kiefer, who is ranked No. 6 and reached the semifinals in his first appearance in this tournament.

Under the tiebreaking formula, Todd Martin and Thomas Enqvist were eliminated. Lapentti and Gustavo Kuerten also failed to advance from the eight-player field.

Sampras, supplanted at No. 1 this year by Agassi, is making his 10th straight appearance at the ATP Championship and has reached the semis the past nine years. Ivan Lendl made 12 straight semifinal appearances, ending in 1991.

Sampras had a tough time with Lapentti. The Ecuadorian saved three set points in the 12th game, two of them on errors by Sampras. Sampras lost the first point of the tiebreaker but won the next six. He wasted one more set point before firing an overhead smash.

Sampras failed to convert 11 break points. He also played sloppily in the second tiebreaker but set up a match point with his 11th ace. He closed the match with a forehand winner.