Sabalenka won four of the first five games and a second break of serve was enough to pocket the opening set.
The Belarusian led 4-2 in the second set but was broken when serving for the match a few games later. She responded right away though with another break before sewing up victory at the second attempt.
With her win, she ended what was a stunning run of form for Svitolina, who had won her previous 11 matches without dropping a single set.
Sabalenka is the first WTA player to reach 30 match wins this season and is through to her fourth final in five years in Madrid, having won the tournament in 2021 and 2023 before losing to Swiatek last year.
In the decider, she'll face world number four Coco Gauff after the American brushed aside reigning champion Iga Swiatek.