Serena Williams of the United States makes a return to Venus Williams of the United States.; Serena Williams of the United States, left, hugs her sister Venus Williams of the United States after winning their singles match, at the All England Lawn Tennis Championships in Wimbledon, London, Monday July 6, 2015. Serena Williams won 6-4, 6-3. (AP Photo/Alastair Grant)

(Updated 7/6/2015) LONDON (AP) — Serena Williams extended her mastery over big sister Venus, and kept alive her bid for Grand Slam history.

In the 26th career meeting between the siblings, Serena dominated with her steady serve and big hitting from the back of the court to win 6-4, 6-3 on Centre Court, extending her Grand Slam winning streak to 25 matches.

The win sent the top-ranked Serena into the Wimbledon quarterfinals as she bids for a fourth straight Grand Slam title, a feat last accomplished by the younger Williams in 2003.

If Serena can triumph again, only the U.S. Open would stand in her way of becoming the first player to complete a calendar-year Grand Slam — a sweep of all four majors in the same season — since Steffi Graf in 1988.

When Venus hit a backhand long on break point to end the match, Serena showed no emotion and did not celebrate. She walked slowly to the net, where the two sisters hugged. They walked off the court together.

“It’s hard to feel excited about (beating) someone you root for all the time no matter what and who you love so much and she’s your best friend in the world,” Serena said. “It’s never easy but you just play for the competition and enjoy the moment.”

Both sisters have won Wimbledon five times, but Serena also has a total of 20 Grand Slam titles. Another Wimbledon title will put her just one behind Graf, who holds the Open era record with 22.

“It was really good for me to get it done in straight sets, and just put this behind me and just move forward,” Serena said.

Monday’s victory improved her career record against Venus to 15-11, including 8-5 in Grand Slams and 4-2 at Wimbledon. This was the sisters’ first meeting at a major since the 2009 Wimbledon final, which was won by Serena.

Serena broke twice in each set and lost serve just once. She had 10 aces, as well as 36 winners and 13 unforced errors.

Venus Williams, playing in her 18th Wimbledon, was the oldest woman in the draw at 35.

This was the earliest all-Williams match in a Slam since they met in the fourth round at the 2005 U.S. Open. Venus was asked whether it felt different playing her sister at such an early stage.

“It’s definitely anticlimactic if this isn’t a semifinal or a final,” she said. “It’s different. Especially when she’s going for something this historic, which is achievable for her.”

Serena will next face another familiar opponent — Victoria Azarenka, the two-time Australian Open champion from Belarus. Azarenka beat 18-year-old Belinda Bencic of Switzerland 6-2, 6-3.

Williams holds a 16-3 career advantage against Azarenka, including a 9-0 record in Grand Slam matches.

Serena was one of three American women to reach the Wimbledon quarterfinals Monday, along with CoCo Vandeweghe and Madison Keys. It’s the first time that’s happened since 2004 when Jennifer Capriati, Lindsay Davenport and Serena made it to the final eight.

The 47th-ranked Vandeweghe surprised French Open runner-up and sixth-seeded Lucie Safavora 7-6 (1), 7-6 (4). Vandeweghe had never gone past the third round of any major until this year’s Wimbledon.

“I’m not really considering it like, ‘Wow, a breakthrough,’” she said. “I had set goals of what I wanted to do, and because I’m achieving it doesn’t mean it’s a breakthrough.”

Vandeweghe will next face fourth-seeded Maria Sharapova, the 2004 champion who downed Zarina Diyas of Kazakhstan 6-4, 6-4. Sharapova has not dropped a set so far, losing only 23 games in four matches.

The 20-year-old Keys got to the Wimbledon quarterfinals for the first time, beating 122nd-ranked Olga Govortsova of Belarus 3-6, 6-4, 6-1. Keys, who reached the semifinals at the Australian Open this year, has now beaten three players here who were ranked outside the top 100.

“I definitely feel like when I’m walking out onto the courts, not only do I feel people are expecting me to win but I am expecting me to win,” Keys said.

In early men’s play, Richard Gasquet held off 20-year-old Australian Nick Kyrgios 7-5, 6-1, 6-7 (7) 7-6 (6) to advance to the Wimbledon quarterfinals for the first time since making it to the semifinals in 2007.

Vasek Pospisil came from two sets down to overcome No. 22 Viktor Troicki 4-6, 6-7 (4), 6-4, 6-3, 6-3. Pospisil is the third Canadian man to reach the quarterfinals at Wimbledon, after Robert Powell (1908, ’10, ’12) and Milos Raonic (2014).