WIMBLEDON, England — Serena Williams won her sixth Wimbledon women’s championship Saturday, overcoming a difficult opening to defeat Garbine Muguruza of Spain 6-4, 6-4.

That gave Williams what she calls the “Serena Slam,” for a second time in her career, four major championships in order, the 2014 U.S. Open, the Australian Open, the French Open and Wimbledon.

It also puts her in position to become the first person since Steffi Graf in 1988 to win the Grand Slam, all four majors in a calendar year.

The final one is the U.S. Open, beginning the end of August, at Flushing Meadows in New York.

First Lady Michelle Obama congratulated Williams via Twitter:

“Wow! Huge congrats to @SerenaWilliams for her win at Wimbledon. We’re all so proud of you! -mo”.

On Sunday, Roger Federer will play Novak Djokovic in his bid for a record eighth Wimbledon title in a rematch of last year’s final. Djokovic beat Federer in five sets last year.

Throughout Wimbledon, Williams put a finger to her lips when someone asked about either the Serena Slam or Grand Slam. But after her singles win, the 21st major — one fewer than Graf — she opened up.

“Man it really is a great feeling,” Williams said. “Just the moment is still setting in a little bit. I’m just really excited about it because I didn’t want to talk about the Serena Slam.”

Williams recorded that a first Slam in 2002-03, after missing the ’02 Australian Open because of an injury and then winning the next four.

“You know what, I feel like I’ll be OK,” Serena said. “If I can do the Serena Slam, I’ll be OK heading into the Grand Slam. I had a really tough draw here. This gives me confidence.”

Williams, No.1 in the rankings and seedings, was a heavily favorite over Muguruza, even though a year ago, Muguruza, a clay court specialist, beat Williams in the second round of the French Open.

On Saturday, on the grass of the All-England Lawn Tennis Club, Williams served to open, had three double faults and was broken. When Muguruza held, Williams trailed by two games. It was 4-2 when Williams took over, winning the next four games and the set.

“She started out well,” Williams said of Muguruza. “Then I started to understand what she was doing, better. I thought, ‘I need to do this.’ I had a problem to solve.”

For the 20th-ranked Muguruza, the problem was Williams.

“With Serena, if you lose two points you lose the match,” Muguruza said.

When Muguruza was given the second-place award, the Centre Court crowd, appreciative of the effort, gave her a long ovation and she started wiping away tears.

“I felt special,” she explained.

Williams is special.

The last major match she lost was to Alize Cornet last year at Wimbledon. Since then, it’s been 7-0 in the U.S., Australian, French and Wimbledon.

“I feel I’m more fit and can do more than 10-12 years ago,” said Williams, who some two months from here 34th birthday became the oldest woman to win Wimbledon.

Williams’ path this Wimbledon included sister Venus, who is 35 but a former Wimbledon champion, and Victoria Azarenka, who was No. 1 and won two Australian Opens. Serena lost sets to Heather Watson and Azarenka but rallied, or more accurately steadied.

“The toughest thing to accomplish is to stay in the moment,” Williams said. “It’s easy to go out and say I want to win, then try to win. But you have to win seven matches. You have to win each match. You have to win each set. You have to win each point.”

Asked how she could do it, Williams, sounding like a commercial for the shoe company she endorses: “You just do it.”

Williams seemingly believes Muguruza soon will be doing it.

“She came out there to win,” Williams said. “She wasn’t out there just to play a final. I think that says a lot about her and her future.”

As far as Williams’ future, it could get very interesting.

Asked to put into perspective the chase for the Grand Slam, she said: “It’s huge, really huge. Of course, I haven’t done it. I’m going to try my best, but I don’t have the Grand Slam in my hands.”