The last year's Madrid finalist will have another chance to fight for the title in the Spanish capital, defeating the 8th seed Sloane Stephens 6-2, 7-5 in an hour and a half for the 11th WTA final and the second of the season.
The Dutch scored the first win over the American in three meetings, playing better on both the first and second serve and fending off eight out of nine break points to mount the pressure on Stephens who competed in the fourth semi-final on the European clay.
Playing against ten break points, Sloane got broken four times, wasting three set points on the return in the tenth game of the second set and dropping the last three games to propel Kiki into the title match. Bertens broke in the very first game of the encounter when she forced an error from Stephens, repelling four break points in the next game to cement the lead and settle into a fine rhythm.
A forehand down the line winner sent Kiki 4-1 up after 20 minutes and she closed the opener with a hold in game eight after 34 minutes. After five good holds in set number two, Stephens drew first blood in the sixth game with a backhand down the line winner, only to waste the advantage in the very next game after a double fault, bringing Kiki back to the positive side of the scoreboard.
Facing an ultimate challenge, the Dutch managed to stayed focused and save three set points at 4-5 to build the momentum and confidence, scoring a break in the next game after a backhand error from Sloane and wrapping up the triumph on own serve following another backhand mistake from the American, moving a win away from the place in the top-5 for the first time.