Top-seeded Caroline Wozniacki reached the Tournament of Champions final after beating Bulgaria's Tsvetana Pironkova 6-4, 6-1 on Saturday.
In Sunday's final, Wozniacki will play second-seeded Nadia Petrova of Russia, who defeated Roberta Vinci of Italy 6-7 (8), 6-1, 6-4 in a match that lasted 2 hours, 42 minutes.
"At one moment in the match I thought that I am playing my last match here and that's why I decided to do my best," Petrova said. "On Sunday, I will try to impede Wozniacki. If I win the title, it will be the perfect end of the season for me."
Supported by an enthusiastic crowd in Sofia's Arena Armeec Hall, Pironkova matched Wozniacki at the start of the first set.
Tied 4-4, the Dane won seven consecutive games to lead 6-4, 5-0.
"I feel sorry to beat Pironkova in front of her fans at home but I am happy to reach the final and hope the fans will support me on Sunday," Wozniacki said.
One fan she could count on was world No. 1 golfer Rory McIlroy, who was in Sofia to support his Danish girlfriend.
Playing for her third WTA title of the year in her fourth final has ensured Wozniacki will return to the top 10 when the rankings are updated on Monday. She will rise from No. 11 to No. 10, switching places with Marion Bartoli.
Petrova will also be trying for her third title of the year. She has lost her past four matches with Wozniacki.