LONDON -- Serena Williams let herself briefly bask in the joy of a sixth Wimbledon championship, 21st Grand Slam singles trophy overall and fourth consecutive major title Saturday, even balancing the winner's silver dish atop her head -- Look, Ma, no hands! -- as she sauntered off Centre Court.

"I was peaceful, feeling really good," Williams said. "Maybe a little after that, I started thinking about New York."

On to the next one. When the U.S. Open begins at Flushing Meadows in August, Williams will pursue pretty much the only accolade to elude her so far: a calendar-year Grand Slam, something no one has accomplished in tennis in more than a quarter-century.

She will arrive there having won her past 28 matches at major tournaments, the latest coming at the All England Club on Saturday, when the No. 1-seeded Williams put aside an early deficit and a late lull, closing out a 6-4, 6-4 victory over No. 20 Garbine Muguruza of Spain.

It's Williams' second self-styled "Serena Slam" of four majors in a row; she also did it in 2002-03.

"I've been trying to win four in a row for 12 years, and it hasn't happened. I've had a couple injuries. You know, it's been an up-and-down process," Williams said. "I honestly can't say that last year or two years ago or even five years ago I would have thought that I would have won four in a row."

At 33, she is the oldest woman to win a Grand Slam tournament in the Open era of professional tennis, and it comes 16 years after her first, at the 1999 U.S. Open.

Only Maureen Connolly in 1953, Margaret Court in 1970, and Steffi Graf in 1988 have won all four majors in a single season. And only Court (24) and Graf (an Open-era record 22) own more Grand Slam singles titles than Williams.

Her collection includes a half-dozen trophies each from Wimbledon, the U.S. Open and Australian Open, and three from the French Open.

"I just never dreamt I would be out here still," Williams said, "let alone winning."

Hasn't come easily. Far from it. At the French Open, fighting an illness, she gutted out five three-setters on the way to the title last month. At Wimbledon, she was two points from defeat twice against Britain's Heather Watson in the third round, then eliminated a trio of women who are former No. 1s and own multiple major titles: her older sister Venus, Victoria Azarenka, and Maria Sharapova.

"She refuses defeat. She refuses to lose," said Williams' coach, Patrick Mouratoglou, who has helped her win eight of the past 13 Grand Slam tournaments. "When she feels the taste of losing, she finds so much strength, and then she can raise her level."

If Serena Williams wins the US Open, she will become the first person to win a calendar-year Grand Slam since Steffi Graf in 1988. Shaun Botterill/Getty Images

Maybe the most telling statistic about Williams' ability to turn it up a notch when the spotlight is brightest is this: Her record in major semifinals and finals is 47-7.

Saturday's victory made her 21-4 in Slam title matches; it was the 21-year-old Muguruza's first major final.

But Muguruza's 6-2, 6-2 win against Williams at the 2014 French Open is the American's most lopsided loss at a major.

In the first game Saturday, Williams contributed three double-faults -- she wound up with eight -- and missed a forehand long, then a backhand long, to get broken. Less than a half-hour in, Muguruza led 4-2, thanks in part to her big, flat groundstrokes that pushed Williams around.

Williams was not going to go gently, of course, and she produced a 20-minute burst of brilliance, grabbing five straight games and nine of 10.

"I was like, `What can I do?" Muguruza said.

Suddenly, Williams was up a set and 5-1 in the second.

And suddenly, she began to come undone.

"All the people are nervous, even Serena, in a final," Muguruza said. "Because I saw it."

Up in the stands, Mouratoglou saw it, too, noticing that Williams' ball tosses on serves were too low, a sign of being tight.

She got broken at love to make it 5-2. After Muguruza held, Williams served for it again, and was broken again, wasting a match point in the process. Now it was 5-4, and the crowd was roaring after each point -- even during some.

"Definitely a little pressure," Williams acknowledged, "toward the end."

Ah, but no one is better with so much at stake. The finish was anticlimactic, with Muguruza missing a forehand to get broken at love. Both women stood still, neither realizing it was over. Soon enough, though, Williams was telling a teary-eyed Muguruza: "Don't be sad, you'll be holding this trophy very, very soon, believe me."

For now, Williams is keeping all the hardware to herself.