<p class="title">A confident Sloane Stephens stormed into a semifinal slot at the WTA Finals with a convincing straight sets victory against top seed Angelique Kerber on Friday, joining fellow debutant Kiki Bertens in the knockout stage.</p>.<p class="bodytext">The former US Open champion continued her unbeaten run in Singapore with a 6-3, 6-3 triumph in 101 minutes, her fifth straight-set victory in a row over Kerber.</p>.<p class="bodytext">After topping Red Group, Stephens will play Czech Karolina Pliskova in the semifinals.</p>.<p class="bodytext">For the first time since 2003, none of the top four seeds advanced to the semifinals of the WTA Finals.</p>.<p class="bodytext">"I stayed solid the whole time knowing there was a lot on the line," Stephens said after the match.</p>.<p class="bodytext">"I knew it was going to be a battle and just tried to play as hard as I could."</p>.<p class="bodytext">The match started tensely, with Kerber unable to convert seven break points in Stephens' first three service games, and the missed opportunities proved costly.</p>.<p class="bodytext">An energetic Stephens made her pay by converting all three of her break points to draw first blood.</p>.<p class="bodytext">The American impressively counterattacked and pinpointed the lines to frustrate Kerber, who survived an injury scare when she landed awkwardly midway through the first set.</p>.<p class="bodytext">Kerber was immediately under pressure in the second set and saved seven break points in the fourth game before cracking under the pressure.</p>.<p class="bodytext">There was still fight left in the German, who broke straight back but continued to struggle on serve.</p>.<p class="bodytext">On her fifth break point, Stephens claimed the decisive break in the eighth game and then served it out to knockout the Wimbledon champion.</p>.<p class="bodytext">Bertens faces unbeaten Elina Svitolina after a hamstring injury forced Naomi Osaka's retirement earlier on Friday.</p>.<p class="bodytext">She won the first set 6-3 in 47 minutes before US Open champion Osaka, who wiped away tears, forfeited the match.</p>.<p class="bodytext">It was a bitterly disappointing end for the 21-year-old, who came into Singapore as the form player but lost three-set matches to Stephens and Kerber.</p>.<p class="bodytext">"I hurt my left hamstring in the first match (against Stephens)," Osaka told reporters.</p>.<p class="bodytext">"It was just getting worse and worse every time I played. I couldn't even really practice that well today."</p>
<p class="title">A confident Sloane Stephens stormed into a semifinal slot at the WTA Finals with a convincing straight sets victory against top seed Angelique Kerber on Friday, joining fellow debutant Kiki Bertens in the knockout stage.</p>.<p class="bodytext">The former US Open champion continued her unbeaten run in Singapore with a 6-3, 6-3 triumph in 101 minutes, her fifth straight-set victory in a row over Kerber.</p>.<p class="bodytext">After topping Red Group, Stephens will play Czech Karolina Pliskova in the semifinals.</p>.<p class="bodytext">For the first time since 2003, none of the top four seeds advanced to the semifinals of the WTA Finals.</p>.<p class="bodytext">"I stayed solid the whole time knowing there was a lot on the line," Stephens said after the match.</p>.<p class="bodytext">"I knew it was going to be a battle and just tried to play as hard as I could."</p>.<p class="bodytext">The match started tensely, with Kerber unable to convert seven break points in Stephens' first three service games, and the missed opportunities proved costly.</p>.<p class="bodytext">An energetic Stephens made her pay by converting all three of her break points to draw first blood.</p>.<p class="bodytext">The American impressively counterattacked and pinpointed the lines to frustrate Kerber, who survived an injury scare when she landed awkwardly midway through the first set.</p>.<p class="bodytext">Kerber was immediately under pressure in the second set and saved seven break points in the fourth game before cracking under the pressure.</p>.<p class="bodytext">There was still fight left in the German, who broke straight back but continued to struggle on serve.</p>.<p class="bodytext">On her fifth break point, Stephens claimed the decisive break in the eighth game and then served it out to knockout the Wimbledon champion.</p>.<p class="bodytext">Bertens faces unbeaten Elina Svitolina after a hamstring injury forced Naomi Osaka's retirement earlier on Friday.</p>.<p class="bodytext">She won the first set 6-3 in 47 minutes before US Open champion Osaka, who wiped away tears, forfeited the match.</p>.<p class="bodytext">It was a bitterly disappointing end for the 21-year-old, who came into Singapore as the form player but lost three-set matches to Stephens and Kerber.</p>.<p class="bodytext">"I hurt my left hamstring in the first match (against Stephens)," Osaka told reporters.</p>.<p class="bodytext">"It was just getting worse and worse every time I played. I couldn't even really practice that well today."</p>