NEW YORK -- The game was four deuces old with Venus Williams serving to stay in the first set. She dished up a second serve, but Serena Williams walloped a crosscourt forehand with such fury that her follow through lifted her feet off the ground.

As the roar of the crowd diminished, an enthusiastic fan hollered, "Let's go, Venus!"

That's how it is in Gotham when the Williams sisters play under the lights in Arthur Ashe Stadium. The spectators aren't for either Venus or Serena; they're cheering for the Williamses. The matches between the women -- this was their sixth meeting on Ashe -- are more celebration than an occasion to vent partisan muscle. It's a good thing, too, because the tennis never got in the way of this latest Williams lovefest.

On a brisk Friday evening, Serena beat Venus 6-1, 6-2 in an hour and 12 minutes to reach the fourth round of the US Open. Serena had break points in every game that Venus served and saw 44 percent of her massive serves go unreturned. Not surprisingly, Serena won the battle of winners 34-14.

"I think it's the best match she's ever played against me," Venus said afterward. "I don't think I did a lot wrong. But she just did everything right. Obviously that level is definitely where she's going to want to stay during this whole tournament."

It might be easier for Serena to reach and remain at that level than it seemed when the draw was made on the Thursday before play began. Fans of the Williams sisters uttered a collective gasp when they both ended up in top quarter of the draw. Moreover, that quadrant loomed as the US Open's equivalent to soccer's "Group of Death."

In a biting irony, the sisters who together account for a total of 30 Grand Slam singles titles were seeded No. 16 (Venus) and 17 (Serena) and ended up destined to meet in the third round. That is, if they survived that far.

Serena, 36, is still adjusting to the demands -- and distracting joys -- of motherhood. She powered her way to the Wimbledon final in July. And all seemed well in her world again just five months into her comeback from what had been a complicated, life-threatening childbirth.

But in her next tournament, Serena suffered one of the most shocking -- and unexpected -- losses of her career. She was knocked out of her first hard-court tournament of the summer by Johanna Konta, 6-1, 6-0. A week later, in an emotional Instagram post, she revealed that she was struggling with postpartum depression. She was 1-1 in subsequent matches leading up to the US Open.

But that minefield of a US Open draw now looks more like a field of dreams for Serena. Top-ranked Simona Halep inaugurated Louis Armstrong with a historic loss, becoming the first female top seed at the US Open to lose in the first round. Garbine Muguruza, a former No. 1 and multiple Grand Slam champion who blocked Venus from winning a historic Wimbledon final last summer, was beaten by a 22-year-old Czech qualifier ranked No. 202, Karolina Muchova. And unpredictable but powerful Anastasia Pavlyuchenkova was a first-round loser.

Serena Williams' 6-1, 6-2 win against Venus at the US Open was tied for the most lopsided match in their career head-to-heads. Elsa/Getty Images

All that left Serena with plenty to celebrate following this triumph Friday night. But the winner was subdued in the aftermath, clearly unwilling to indulge to spike the ball at the expense of Venus. Serena said, "It feels good for the match to be over with. Win or lose, it just feels good that that's done."

It's ironic, but perhaps not inexplicable, that Venus was the catalyst enabling Serena to get back in touch with her genius. The only way to handle all the emotions and distractions inherent in this matchup is for the sisters to shut out them out -- along with everything else -- once they step on the court. The focus is as steady as the flame of a Bunsen burner.

"It takes more mental energy than physical," Serena said. "It's not easy, but it is what it is. We started this journey 35 years ago, maybe less." She paused, realizing her math was questionable, but added, "Well, in a way, it started before we were born, so we started this journey a long time ago. We kind of knew what to expect. Even though it's difficult, especially for me, we just do the best that we can."

Being able to reignite that burner will be a valuable skill in the coming days.

If the third-round match against Venus was a nasty, premature surprise, the fourth round must look something like a sunrise to Serena. On the horizon waits Kaia Kanepi, who's ranked No. 44. No. 3 Sloane Stephens is the only player seeded in the top six still in Serena's half of the draw.

"Every match you play, you have to win," Venus said. "[Serena] didn't win that match tonight because I just rolled over. She played untouchable tennis. Whoever she plays, she's going to earn it. It's not like people don't try. People will try against her. I know people are going to keep that up."