World number one Serena Williams said she would have considered 2013 a disappointing year had she not won her fifth US Open title on Sunday.
The defending champion, 31, beat second seed Victoria Azarenka 7-5 6-7 (6-8) 6-1 to claim her second Grand Slam title of the year following her French Open win.
Williams has now won 17 Grand Slam singles titles, seven short of Margaret Court's all-time major record of 24 titles and five from Steffi Graf's Open era mark of 22.
She arrived at Flushing Meadows having won eight titles and enjoyed a career-best winning streak of 34 matches in 2013.
"Absolutely," she said. "I felt almost disappointed with my year, to be honest.
"I won the French Open but I wasn't happy with my performances in the other two Slams - and not even making it to the quarter-finals of one.
"So I definitely feel a lot better with at least a second Grand Slam under my belt this year."
Williams let a double-break lead slip and failed to serve out the match twice in Sunday's final, admitting: "I think I got a little uptight, which probably wasn't the best thing at that moment.
"I wasn't playing very smart tennis then, so I just had to relax and not do that again. But I did it again."
Azarenka battled superbly to force a third set, but Williams regained her poise to dominate the closing stages.
She added: "I thought: 'This is outrageous that I'm still out here, because I had a great opportunity to win already.'
"So I thought: 'You know what? I just have to relax, calm down and play smarter tennis.'"
Williams, who began working with French coach Patrick Mouratoglou last year, turns 32 later this month, but retirement remains some way off.
"I feel great," she said. "I have never felt better. I feel really fit. I can play a tournament like this, singles, doubles, with tough, tough schedules. For the most part, I felt really good.
"I haven't felt like this in a number of years - I'm excited about the possibilities. I don't know what can happen. I just keep playing and do the best that I can."
Mouratoglou says Williams's determination to prove her ability every time she steps on court makes her unique in tennis.
"She is a champion; it is difficult to explain what is in the mind of a champion," he said.
"She feels she is the best and this self-confidence in her game gives her the will to prove it to herself every day on the court. She is Serena Williams and there is only one."
Former US President Bill Clinton described Williams as an inspiration to others.
"She always wanted to be someone who opened up new avenues for girls and women," he said.
"She is able to play highly competitive, high concentration tennis and win, but always be concerned about why she was really doing it."
Azarenka, 24, fought valiantly to force a decider but could not keep the pressure on Williams as she had in the previous set.
"I think it was the moment in the third set that the momentum changed a little bit and I kind of felt like I lost that momentum," said the Belarusian.
"It didn't happen just because I was out of focus or something. She really made it happen. In that particular moment she was tougher today. She was more consistent and she deserved to win.
"The game overall, there are things that could have been better, but I gave my heart. I fought as hard as I could.
"So that's what is important for me - that I lost to a great champion - but I'm still going to have my head up."