Serena Williams staged comebacks in both sets to defeat China's Li Na 7-5 7-5 on Saturday and reach the WTA final at Cincinnati for the first time.
The world No.1, who has claimed 15 titles in the last 16 months and is bidding for her ninth this season, will play either second-seeded Victoria Azarenka or former world No.1 Jelena Jankovic of Serbia.
Li ended in unfortunate fashion, double-faulting on a set point in the first and again on match point in the second.
Williams claimed her eighth win in nine matches against Li, who did not played in the previous round as opponent Agnieszka Radwanska withdrew to attend a funeral in her native Poland.
Williams' previous best in Cincinnati was a semi-final in 2006 when it was a smaller women's-only tournament but it's a rare gap in a bulging career resume.
"When you win a lot you develop a lot of confidence and a belief that you can do well," said the 31-year-old.
"I've been training more and enjoying it a lot over the past year and a half."
Williams also won the US Open Series title which gives her a chance at a $US1 million ($A1.10 million) bonus should she win the US Open which begins a week from Monday.
The American admitted to dealing with an abdominal muscle problem this week but did not go into details, saying she did not want to tape it for fear it might hinder her movement.
