LONDON—American Sloane Stephens won the battle of former Grand Slam winners against twice Wimbledon champion Petra Kvitova on Monday, ousting the Czech 10th seed from the All England Club with a 6–3 6–4 victory. The 2017 U.S. Open champion came into the match on Centre Court with a 2–1 head-to-head lead against Kvitova, who lifted…