Serena Williams of the U.S.A. celebrates after winning her match against Venus Williams of the U.S.A. at the Wimbledon Tennis Championships in London, July 6, 2015.[Photo/Agencies]

LONDON - 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.