Simona Halep delivered her fourth bagel of the Madrid Open en route to securing a place in the final by beating Belinda Bencic in three sets.

Halep will regain the world number one ranking if she triumphs at Caja Magica and is a win away from doing so after coming through a testing encounter with Bencic 6-2 6-7 (2-7) 6-0.

It looked as if it would be a routine victory for Halep, champion in Madrid in 2016 and 2017, after she took the first set 6-2. However, a back-and-forth second went in favour of Bencic, who was making her first semi-final appearance on clay since 2014, the Swiss forcing a decider with a dominant tie-break.

Yet Bencic's momentum completely disappeared in the third as she became the third player in this tournament to be shut out in a set by Halep, who dished out a bagel against Margarita Gasparyan and two in her demolition of Viktoria Kuzmova.

"I think I was rushing a lot in the tie-break, the first point, and when I saw it was 4-0, I lost confidence a little bit," French Open champion Halep said. "But then I just repeated to my head that the match is starting now, so I have just to focus on the last set, not thinking anymore about the second set.

"All the time when I come to the clay court season, there is an extra motivation and I feel better."

She will face Kiki Bertens, last year's beaten finalist, in the showpiece after the Dutchwoman saw off Sloane Stephens in straight sets.

Bertens was in control throughout the first set and demonstrated fighting spirit that should serve her well in the final to come from a break down in the second, winning five of the next six games to progress 6-2 7-5.

"I know it's going to be a tough battle. I'm ready for it," Bertens said of her final with Halep. "I think I learned a lot from last year [a defeat to Petra Kvitova] – for sure, I will go for it."