Lindsay Davenport's comeback gathered momentum with a 6-4 2-6 6-2 win over top seed Jelena Jankovic in Bali.
Davenport has shown she is still a force to be reckoned with
The American former world number one had reached the quarter-finals in her singles return but was not expected to beat the current number three.
Davenport, 31, quit the WTA Tour last autumn after struggling to shake off a long-term back injury.
The former Australian Open, Wimbledon and US Open champion gave birth to her first child in June.
Neither Davenport nor her Serbian opponent played well but the American's serving power gave her the edge over a weary-looking opponent.
I didn't train much and it's tough to get motivated here. But it's OK, now I can finally go to the beach
Jankovic became involved in a number of disputes with Sri Lankan umpire Asitha Attygala, especially late in the third set, and refused to shake hands with the official at the end.
"It was a nightmare being out there," she said. "I'm coming from the US Open and we are used to challenges (Hawk-Eye line-calling) at the big matches.
"The umpiring was just terrible. When the ball was in, he called it out, when it was out, he called it in."
Davenport said: "When your opponent self-destructs, that's good from your perspective. I just worried about my own game.
"In professional tennis you have to deal with line calls. When she blew up I knew I had a great shot at winning."