Lindsay Davenport was unable to build on last week's comeback win at the Bali Classic as she lost in the semi-finals of the China Open in Beijing.
Davenport says she will play one more tournament this year
The former world number one's eight-game winning streak was ended as she lost 6-3 7-5 to Jelena Jankovic.
Last week the 22-year-old Serbian was beaten by Davenport last week in Bali.
In the final the world number three faces Hungarian sixth seed Agnes Szavay, who beat China's Peng Shuai 6-1 6-2 in front of a partisan home crowd.
Davenport is making a return to the Tour after a year in retirement and just three months after giving birth to her son Jagger.
"It's been so much tennis for me over the last two weeks and for the first time my legs felt heavy and I couldn't move as quickly as I would have liked to," said the 31-year-old.
It's been a wonderful couple of weeks, I've really enjoyed it and have exceeded my expectations
"But it's been a wonderful couple of weeks, I've really enjoyed it and have exceeded my expectations."
Davenport was a break up in both sets but made 20 unforced errors and Jankovic battled back to beat the American for the first time to claim her place in the final.
"This time it was a different story, I tried to play tight and tried to move her around," Jankovic said.
"I tried not to give her the shots that she likes because it's amazing how clean she hits the ball."
The match became bad-tempered in the second set when Davenport complained to the umpire after being hit by a ball Jankovic had tossed into the air.
"There's no room to act like you're 12 years old, this is the pros," Davenport added.
"I think at 5-5 in the second set when you're about to serve, you shouldn't have to worry about being hit by the ball out of play."
Jankovic said she had apologised to Davenport on court.
"I was really frustrated but it was an accident," she said. "I really apologise, I didn't do it on purpose for sure."
Szavay, who has risen from 207th to 23rd in the world thisyear and won her first WTA title in Palermo in July, will be playing her third final of the season in her first match against