Stan Wawrinka stunned Bulgarian sixth seed Grigor Dimitrov 1-6, 7-6 (7/3), 7-6 (7/5), 6-4 on Centre Court.
The 36-year-old Swiss earned a return to the top when the rankings are updated Monday, by reaching the semifinals in Rotterdam.
Grigor Dimitrov set his sights on winning his first Grand Slam after his dramatic victory at the ATP Finals on Sunday.
Grigor Dimitrov beat David Goffin 7-5, 4-6, 6-3 to become the first debutant to win the season finale since 1998.
David Goffin shocked overwhelming favourite Roger Federer on Saturday in the last four of the ATP Finals.
Grigor Dimitrov struggled to live up to the hype and often found himself written off as a serial underachiever.
Bulgaria's Grigor Dimitrov raced into the semi-finals of the ATP Finals with a 6-0, 6-2 demolition of David Goffin.
Grigor Dimitrov defeated Dominic Thiem 6-3, 5-7, 7-5 in the opening match of the Pete Sampras Group at the ATP Finals.