Halep had led the Pole 5-1 in the tiebreaker of their final round robin clash only to lose the next six points and the set, with the 24-year-old Romanian collapsing in the second and only able to muster a single game.
"I was done. No energy anymore. I was tired," Halep told reporters. "I felt that I lost the chance to win the first set and probably I lost the chance to win the match in that moment."
Halep could have advanced to the semi-finals even in defeat on Thursday if she had won a set after the Romanian split her opening two matches -- a 6-0 6-3 win over U.S. Open champion Flavia Pennetta and 6-4 6-4 loss to Maria Sharapova.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Working out the permutations seemed beyond a clearly exhausted Halep, who was looking forward to enjoying some time away from the court after the straight sets loss ensured there would be no repeat of her run to the final here last year.
"I had the chance in the first set in the tiebreak. That's why I'm a little bit disappointed that I lost this match, because I couldn't finish the first set," she said.
"Then she was dominating. She started to play her best. It was a good match. I was tired. I go home. I just want to take the holiday now. I don't want to think about tennis anymore," she said with a smile.
It marked a premature end to a year of mixed fortunes for the world number two, who was top seed at the elite eight woman event in Singapore after the withdrawal of defending champion Serena Williams due to fatigue.
While Halep won the biggest title of her career at Indian Wells in May and also lifted trophies in Dubai and Shenzhen, she suffered a first-round defeat at Wimbledon and was knocked out at the opening stages of the premier mandatories in Madrid and Beijing.
That followed a second-round loss at the French Open, which the Romanian said was the biggest disappointment of her year.
But she picked up with a strong showing on the American hardcourts and reached the semi-finals of the U.S. Open.
"Yeah, actually, I think I had a good year this year. Ups and downs, but it was okay," she said.
"I will finish number two or three in the world so it's pretty good for me. It's second year in a row.
"I want to get better for the next year. I have many things to improve. I have to run a little bit more because I need. Today I couldn't breathe anymore in the second set."
(Editing by Sudipto Ganguly)
