ISTANBUL - Serena Williams overcame physical problems as well as emotional distress to defeat Jelena Jankovic 6-4 2-6 6-4 on Saturday and reach the WTA Championships final.
The world number one and defending champion, who will face China's Li Na in Sunday's final, put in a stumbling performance and twice sat weeping into her towel during change-overs.
She also committed 40 unforced errors and hit 40 winners and allowed a 5-1 final set lead to evaporate to within one point of 5-5 before finishing the match with three trademark heavy blows.
"I'm relieved and just glad to be in the final," said Williams.
Li earlier beat 2011 winner Petra Kvitova 6-4 6-2 to reach her first final at the event.
Li is unbeaten in four matches in the tournament, after failing to advance from the group stage in the previous two years.
She will rise two places to No.3 in the WTA rankings.
Sunday's final will feature two players over the age of 30.
"The oldest players have more experience on court," said Li.
"This year I was feeling more confident. I understand more what I should do on the court and off it."