Halep lost top spot to Naomi Osaka after the Japanese player won the Australian Open in January but is only one victory away from regaining it after a hard-fought 6-2 6-7 (2) 6-0 success against Belinda Bencic in the Spanish capital.
French Open champion Halep, the winner in Madrid in 2016 and 2017, is regarded as the best clay-court player on tour and she has been in fine form this week, not dropping a set until this match.
— WTA (@WTA) May 10, 2019
Bencic defeated Osaka in the quarter-finals to continue her brilliant 2019 but, after edging the second set, was unable to maintain the required consistency to really threaten a repeat against Halep.
It will be a second straight final appearance in Madrid for seventh seed Bertens, who gained revenge on reigning champion Petra Kvitova in the last eight before defeating Sloane Stephens 6-2 7-5 on Friday.
Stephens battled well in the second set and had chances to take it to a decider but Bertens held on.