She will face off for the title against world number two Victoria Azarenka, who won a match plagued by breaks of serve — 23 in total, including the first six games — to defeat 2011 finalist Jelena Jankovic 4-6, 6-2, 6-3.
Azarenka and Williams will both be playing for their first title at the tournament. Azarenka finally earned her victory with a concluding break of former number one Jankovic.
World number one Williams, who has won 15 titles in the last 16 months and is bidding for her ninth this season, needed just over 90 minutes to advance against the error-prone 2012 winner here.
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 had not played in the previous round when opponent Agnieszka Radwanska withdrew to attend a funeral in her native Poland.
China’s former Roland Garros winner had a bad day on serve, double-faulting on a set point in the first set and ending the contest after 83 minutes with the same costly error on match point.
Williams’ previous best in Cincinnati was a semi-final in 2006 when it was a smaller women’s-only tournament. “When you win a lot you develop a lot of confidence and a belief that you can do well,” said the 31-year-old.