If Serena Williams doesn't wind up as the greatest player in women's tennis history, as she's already being dubbed, she's on track to finish as America's most successful at least.

Williams' gutsy 2-6 6-2 7-5 comeback win over world No.1 Victoria Azarenka in the first women's US Open final to go the full distance in 17 years completed a magical summer treble.

Along with collecting the $US1.9 million winner's cheque, Williams joined older sister Venus and German great Steffi Graf as the only women ever to claim the Wimbledon, Olympic and US Open titles in the same season.

"It's just been fabulous," she said. "I never expected to win all these titles."

Now that she has, Williams has shot past her childhood idol Pete Sampras's 14 career majors with 15 of her own and moved to within three of fellow US legends Martina Navratilova and Chris Evert.

"Well done @serenawilliams. What a gutsy comeback in the third set. You are catching me and Chris, and I don't like it." Navratilova tweeted after Williams twice rallied from a service break down in Sunday's thrilling decider.

Apart from Navratilova and Evert, Williams trails only Helen Wills Moody (19), Graf (22) and Australia's Margaret Smith Court (24) on the women's all-time grand slam singles leaderboard.

The all-conquering American admits she hadn't really considered catching Smith Court "until recently".

"I never thought I would even come close to breaking those records," Williams said.

"But if I can play consistently and play some more matches at Wimbledon, then it will be awesome.

"If I could win two a year, it would be great. We'll see.

"I feel like even though I'm 30, I feel so young and I've never felt as fit and more excited and more hungry."

Williams endured a two-year major title drought before collecting her fifth Wimbledon trophy in July, after lacerating her foot celebrating her 2010 success at the All England Club and then suffering a pulmonary embolism last March.

But the former world No.1 returned to her rampant best during a spectacular 2012, winning 43 of 45 matches since April and picking up six trophies along the way.

Her only defeats have been a shock first-round loss to Virginie Razzano at the French Open and a quarter-final slip-up against Angelique Kerber last month in Cincinnati.

Given her phenomenal form and ability to dominate when fully fit, Williams could be forgiven for believing she could already have surpassed Navratilova and Evert had she not missed 10 slams since winning her first as a 17-year-old in New York in 1999.

"Like in 2010, I was playing really well," she said.

"If I didn't win the US Open, I definitely could have won Australia because I love winning Australia. I definitely think that set me back.

"But there's nothing I can do about that. I've let that go. I don't think about what could have been. I just think about what I have and what I want to do.

"I have so much more I want to create for the history."

The 13-year gap between Williams winning in '99 and her fourth Open now marks the longest span between major triumphs in 45 years of professional tennis.

"Three decades - the '90s, 2000s, 2010s - that's kinda cool," she said.

And to win after Azarenka served for the match at 5-4 in the deciding set made the victory even sweeter.

"I never give up," Williams said. "I never, never quit."

Azarenka, the Australian Open champion who ended Samantha Stosur's title defence in a third-set tiebreaker in the quarter-finals, will retain her top ranking despite the gut-wrenching loss.

"Being so close, it hurts deeply to know you don't have it," the Belarusian said.

"But at this moment, I have no regrets. I felt like I gave it all there."