The sixth seed was beaten 6-3, 6-2 by the twice former champion on a bad day at Flushing Meadows and said her on-court manner was the main reason she missed out on a place in the final.
"I think I was behaving like a really spoilt girl today," Safina told reporters.
"I have to learn from these things if I want to get better. If I want to make one step in front, I have to learn to handle my emotions better."
Safina, runner-up at both the French Open and Olympics, led 2-0 in the opening set but said the windy conditions had contributed to her bad body language.
"I think today I was feeling physically better than previous days but it’s too bad behaviour from my side.”
"Maybe I was 80 percent physically and mentally but I spent 60 of it being negative on the court, like shooting around and complaining about everything."
Safina said the way Williams coped with the conditions and the occasion was something she would like to replicate in future.
"I could see she was having some problems at first and I was 2-0 up with a break but she behaved like a champion," she said.
"She also had some wind problems, but she was there and she was fighting with me, and I was fighting with everything around except her. This I can learn from her."
Despite the defeat, Safina said she was on the right track.
"Finally I am playing my game and the results I have are actually what I was dreaming about, to play a grand slam final (at the French Open), and a semi-final again.”
"It is not over yet but it (has been) a great year."