Serena is one of only six women to win nine or more Slams in the Open era
New world number one Serena Williams warned her rivals she had a renewed passion for the sport after capturing her third US Open title.
The 26-year-old's win over Jelena Jankovic earned her top spot in the rankings for the first time since 2003.
"I feel like I have a new career. I feel so young and I feel so energised to play every week," she said.
"I feel there's just so much that I can do in my career yet and I've never felt like I've played my best tennis."
Williams defeated second seed Jankovic 6-4 7-5 in Sunday's final, which had been delayed from Saturday because of heavy rain.
Jankovic, who would have become world number one with victory, had four set points in the second set but Williams came through to wrap up her ninth Grand Slam title.
Williams, who last won the US Open in 2002, put her renaissance down to a new dedication to fitness.
I love winning Grand Slams
"I've been working so hard all year. Sometimes I wake up at like six in the morning to go practice and if it was too dark, I would have to wait until it gets light," she said.
"It's just paying off. No one really, really knows the work that an athlete puts in. You know, it's worth it. Then I felt like, 'Gosh, I've been working the hardest. I should win'."
Williams did not drop a set at the tournament as she became only the sixth woman in the Open era to win nine or more Grand Slam titles.
"This is cool, because I'm at number nine. I'm knocking at the door of double digits," she said.
"I have the game to do it. I obviously play well in Australia, and that's coming up soon, so maybe there. I have to win another French Open and I love Wimbledon. I love winning Grand Slams, so I look forward to it."
Jankovic, 23, declared herself satisfied with her efforts after reaching her first Grand Slam final.
"I had a great two weeks," she said.
"I really fought hard out there every match and tonight I gave everything I had. Unfortunately it was not enough."
However, Jankovic admitted she was annoyed that Williams had been allowed too much time between points as the American tired in the second set.
"I felt she was tired and I really had my chances," she said.
"I really was a little bit upset about the umpire, you know. She (Williams) took quite a lot of time in between the points and I thought it was not fair.
"She took her time to recover and get back. But you can talk all day about this. I lost, she won. That's what counts."