Now she has that Olympic double — just like Venus.
The overpowering American pair won the doubles title at the Olympics on Sunday, with Serena adding to the singles gold she won on Centre Court at Wimbledon a day earlier.
"Crazy," Serena said. "I'm always copying her. I forgot that she did it in Sydney and I do it here. We're the same doubles team, we just split this to singles, so it's cool."
The sisters beat Andrea Hlavackova and Lucie Hradecka of the Czech Republic 6-4, 6-4 under the roof on a rainy afternoon at the All England Club. Venus — with her red, white and blue braids pulled back into a bun — closed the match on the very grass she has long loved with a backhand volley winner after the Czechs saved a pair of match points.
"We all talk about this, 'We have so many medals,' but to be able to add to that, it's like an unbelievable feeling," Venus said. "You know that in that count, there you are. It feels amazing."
On Saturday, Serena beat Maria Sharapova 6-0, 6-1 for the singles gold. She joined Steffi Graf as the only women to complete the Golden Slam — winning the Olympics and the four majors.
When the Americans in the crowd at Centre Court broke into a chant of "U-S-A! U-S-A!" as the players left the court, the sisters pumped their fists, turned to wave, then slapped a high-five. This was another commanding performance — as the sisters didn't drop a set through their five matches in London.
The medal ceremony had to wait some five hours after the outdoor bronze-medal match which was delayed by rain — and both sisters literally let their hair down for their moment on the podium. Venus sported bright red lipstick, and Serena put her arm around her sister's waist and embraced her from the side.
Third-seeded Maria Kirilenko and Nadia Petrova of Russia took the bronze by beating the top-seeded U.S. pair of Liezel Huber and Lisa Raymond, 4-6, 6-4, 6-1.
With Bob and Mike Bryan taking the gold in men's doubles Saturday, U.S. tennis made it three golds in two days.
"I feel great to be a part of this U.S. team this year," Venus said.
Serena became tennis' first double gold medallist at an Olympics since Venus won singles and doubles at the 2000 Sydney Games. The sisters also won the doubles gold at the 2008 Beijing Olympics. And with Sunday's victory, each has a record four Olympic tennis gold medals.
While Serena was thrilled to win on her own Saturday, with Venus cheering from the family box, the doubles is what she most cared about coming to London. Especially considering all the emotional and physical struggles for Venus, who was diagnosed last year with an autoimmune disease that causes fatigue.
"This is all I wanted," said Venus, who had all of about two months to raise her ranking and qualify for the Olympics. "Boy, was that a battle. That was one of the hardest things I've ever done. I really feel proud of what happened here at the Olympics."
It was one more triumph for a player who has won five of her seven Grand Slam titles at Wimbledon.
"Venus has been going through so much and she's so strong and so she's so amazing," Serena said. "And to win this was my goal."
The Williamses are the first tennis players to win Olympic gold indoors since the 1912 Stockholm Games, a match played in a pavilion on wood courts painted black.
Venus Williams joins Conchita Martinez of Spain as the only tennis players to win medals at three Olympics. Martinez's medals all came in doubles — silver in Barcelona in 1992, bronze in Atlanta in 1996 and silver in Athens in 2004.
Gigi Fernandez and current U.S. coach Mary Joe Fernandez are the only others to win back-to-back Olympic tennis gold medals after they teamed for doubles titles in 1992 and 1996.
And the sisters insist they're not done yet.
"We're looking forward to Rio," Serena said, "and trying to get some sort of medal there."