Sloane Stephens rolled into the semifinals as she defeated top seed Angelique Kerber 6-3, 6-3 to complete round robin play in the Red Group at the 2018 WTA Finals.
The American blasted 25 winners en route to her fifth straight victory over the German, who committed 38 unforced errors in the 1 hour, 40 minute match.
Stephens takes ninth straight set from Kerber
Both players struggled in their opening service games with Stephens saving two break points and after Kerber held easily for a 2-1 lead, the fifth seed was under pressure again.
She fended off five break points, saving them with some spectacular winners to hold for 2-2. In the reigning Wimbledon champion's next service game, the American blasted an overhead winner at 15-40 to claim a 3-2 lead.
Kerber was becoming wasteful on her break chances and she failed to convert two more in the sixth game, one of them saved by Stephens with a brilliant backhand winner.
After squandering her first seven break points, the German let down, dropping serve to give Stephens a 5-2 lead, but she squandered three set points as Kerber finally broke to cut the deficit to 5-3.
Her efforts were ultimately futile as she fell behind 15-30. After an errant drop shot brought up two set points for the American, Stephens took advantage, firing a deep backhand to force an error from the German and grab a one-set lead.
American continues fine form, reaches last four
The rallies continued to be grueling as the second set got underway with games getting longer. Kerber saved a break point in the second game and Stephens held for a 2-1 lead courtesy of her backhand.
In the next game, 22 points were played and on her seventh break opportunity, Stephens converted when Kerber missed a drop shot to hand the American a 3-1 lead.
The German was back on serve as the Miami champion surprisingly faltered, making a number of unforced errors and wasted three game points to see her advantage disappear.
Kerber faltered on serve one final time trailing 4-3. The German saved three break points as her forehand briefly caught fire, but Stephens reached a fourth chance after a backhand error by Kerber.
After Kerber punched a forehand miscue into the net, the American led 5-3 and served for the match. She reached 40-0 and after the German drove a final backhand, Stephens sealed her semifinal spot opposite Karolina Pliskova.