MADRID—Aryna Sabalenka is glad she changed her mind about playing at the Madrid Open. Two weeks after nearly withdrawing from the tournament because of a muscle injury, Sabalenka was standing on center court with the winner’s trophy in her hands on Saturday. Sabalenka defeated top-ranked Ash Barty 6-0, 3-6, 6-4 for her 10th WTA title—and…