It was the sisters' earliest meeting in a tournament since the second round of the 1998 Australian Open.
It's always a big story when the Williams sisters compete on the court, with the younger sibling now holding an 17-12 lead in the all-time series. She served very consistently.
Into the second set, Venus broke Serena again in the opening game then again in the third to take a 3-0 advantage and eventually hold on to win the set and the match despite a late 4-game rally by Serena. Like I said, I have had a few more matches.
"It's good that I don't have to say that this is the best tennis I have ever played and I lost", Serena said. "Even though I haven't even played that much this year, the matches in the last year count".
Venus is now positioned to be the top contender to win this week at Indian Wells Tennis Garden in California.
Venus thus wasn't dwelling on her win Monday.
The 10th seeded Venus moves on to the round of 16 where she will face either Anastasija Sevastova or 12th seeded Julia Georges.More news: No coordination between Trump and Russia, say Republicans in draft report
Venus's victory also comes 17 years after an ugly booing incident led to a 14-year boycott of the tournament by the sisters.
"But I call this a trial run, you know".
Typically, the sisters wouldn't meet until the later rounds of a tournament. Serena ended the match with a forehand failing to find the court, one of her 41 unforced errors.
"I'm getting there", she said. During Serena's year-long hiatus, Venus carried the torch.
Elsewhere, Australian Open champ Caroline Wozniacki benefited from a challenge call in the final game en route to defeating Aliaksandra Sasnovich 6-4, 2-6, 6-3.
"She put very high pressure on Serena from the start, playing fast and aggressive and with a lot of success", Mouratoglou said. It's definitely not less disappointing, I wish it was.
"So I have just got to keep saying at each tournament that my goal is just to be better than the last. I want to continue to go forward". "I'm playing a completely different player, new challenges". She said their father, Richard, would probably decide - an insinuation that their matches were rigged.