The American will finish 1998 as world number one for a record sixth successive year after rival Marcelo Rios pulled out of the tournament in Hanover due to back trouble.

He celebrated by trouncing Kucera 6-2 6-1 in only 45 minutes in his final Red Group match.

Sampras came into the event with a slender 33 point lead in the ranking list, but underlined his determination to hang onto top spot with comfortable straight sets wins over Yevgeny Kafelnikov and Carlos Moya in his first two round robin matches.

Rios was the only man who could have replaced him as number one, but complained about a sore back following his defeat by Britain's Tim Henman on Tuesday.

He was expected to play his second match against Greg Rusedski but organisers revealed he had withdrawn from the event, less than an hour before they were due on court.

"I waited until the last minute. I went to bed last night thinking I would play. But when I tried to practice this morning, it was really sore. It made no sense to go out on court and play two games," said Rios.

"I'm disappointed but that's the way it goes. It's so sore that I can't go on court. Pulling out of tournaments is always bad."

Sampras previously shared the record with Jimmy Connors, who was world number one from 1974 to 1978.