Cincinnati: Serena Williams came from a break down in the opening set to produce a patchy 6-4, 6-3 win over Elina Svitolina and reach the WTA final in Cincinnati on Saturday.
The top-seeded world number one was far from efficient, appearing to lose her way on some shots.
Nevertheless, Williams will bid for her second straight Cincinnati title on Sunday, facing the either third-seeded Simona Halep of Romania or former champion Jelena Jankovic of Serbia.
The 33-year-old Williams -- who will be trying to finish a rare calendar Grand Slam when the US Open begins on August 31 -- offered no explanation for her patchy form.
"I don`t know how I turned the match around," she said. "I got off to a super slow start.
"But I managed to start going for my shots and that helped me out. I just told myself to dig deep."
Williams won her 47th match against just two defeats this season.
The 21-time Grand Slam singles champion improved to 20-4 at Cincinnati, the last major event prior to the start of the year`s final Grand Slam at Flushing Meadows.
She will be playing her third Cincinnati final in a row and for her fifth title this season. She hammered nine aces but had eight double-faults on her way to victory.