Clijsters first became world number one in 2003
Kim Clijsters will replace Caroline Wozniacki as world number one on Monday after beating Jelena Dokic 6-3 6-0 in the quarter-finals of the Paris Open.
Clijsters, 27, has held top spot three times before, twice in 2003 and once in 2006 before retiring in 2007 to have a child, only to make a stunning return.
The Belgian won the 2009 US Open, retaining the title last year and then adding the Australian Open this year.
Her next opponent is Kaia Kanepi, who beat Dominika Cibulkova 6-2 2-6 6-2.
Having lost the first four games of her match against Kristina Barrois on Wednesday, Clijsters was again slow out of the blocks against Dokic, going 3-0 down early on before finding her rhythm with her serve and dominating her opponent at the net.
In the second set Dokic was hitting the ball harder, but top seed Clijsters was in full control of the match and eased to victory as her opponent crumbled under the pressure.
Afterwards, Clijsters said age and experience enabled her to get more satisfaction out of her success second time around.
"I'm able to enjoy all the things that are happening now in a different way," she said.
"I'm able to share it with a bigger group and with my team. That's what I enjoy the most about this second career."
The other semi-final will be between world number 48 Bethanie Mattek-Sands, who beat Germany's Andrea Petkovic 7-6 2-6 6-3, and fourth seed Petra Kvitova.
The Czech player secured her place in the last four with a 5-7 6-3 7-6 win over Yanina Wickmayer.