Mark Talbott, a relatively unknown player from Dayton, Ohio, defeated legendary champion Sharif Khan, 16-14, 9-15, 15-11, 15-10, in the final of the $15,000 Boodles Squash Open last night at the Capitol Hill Squash Club.

Few of the 150 spectators at the 1-month-old club expected Talbott to win the $3,000 prize by upsetting the 35-year-old winner of four previous Boodles Open crowns, even though he beat the first, third and fourth seeds earlier in the tournament.

Khan, considered "the Bjorn Borg of squash," lost his No. 1 ranking this year for the first time in 11 years to Michael Desaulniers, who defeated him four of six times in 1980. Talbott defeated the top-seeded Desaulniers in a 1 1/2-hour semifinal match earlier yesterday.

En route to the final, Talbott, 20, defeated three of the top four tour players in the World Professional Squash Association rankings: 1980 North American pro champion Clive Caldwell, former Harvard collegiate champion Desaulniers and 1979 professional champion Stu Goldstein.

"If there ever was a giant killer, he's it." Khan said after Talbott's victory. "The star of the future has become the champion today."

Fifth-seeded Gordon Anderson, who lost to Desaulniers in the consolation match, called Talbott "the wave of the future in professional squash. Let's all hope we can catch up to him."

Talbott, whose brother Dave also plays on the tour, was ranked 11th going into the tournament in this, his first year as a pro. This was the first time he reached a tournament final, and the first time he has defeated Khan in four tries.

"Sharif and I both live in Toronto and we practice about two or three times a week," said the boyish champion. "I knew his game and I thought I could beat him with my consistent shots up and down the walls and my speed." i

Talbott stuck to his plan, running down every Khan drop shot and pounding his returns deep and close to the wall. It was a classic confrontation between youth and experience, and this time youth won.