For stretches of the 27th edition of Williams vs. Williams, Venus gave Serena all she could handle.

And when Serena took control down the stretch to emerge with a 6-2, 1-6, 6-3 victory in a well-played U.S. Open quarterfinal, allowing her to continue pursuing the first calendar-year Grand Slam in more than a quarter-century, a smiling Venus wrapped both arms around her little sister for a warm hug at the net and whispered, "So happy for you."

"Obviously we are very, very tough competitors on the court," Serena said later, "but once the match is over, the second it's done, you know, we're sisters, we're roommates, and we're all that."

Serena called their unique sibling rivalry "the greatest story in tennis," and who would argue? A couple of kids taught by their dad on cement courts in Compton, California, making it all the way to the top.

With two more match wins, the No. 1-ranked Serena would become the first player since Steffi Graf in 1988 to collect all four Grand Slam titles in a single season. Plus, if she can win what would be her fourth U.S. Open in a row, and seventh overall, she would equal Graf with 22 major championships, the most in the professional era and second-most ever behind Margaret Court's 24.

"That would be huge, not just for me, but for my family, just for what it represents and how hard we have worked and where we come from. So it would be a moment for our family," said the 23rd-seeded Venus, who is 15 months older. "But at the same time, if it doesn't happen it's not going to make or break you. We don't have anything to prove. She has nothing to prove. She's really the best ever."

Serena is 16-11 in their all-in-the-family matches, including 9-5 in majors and 3-2 at the U.S. Open. And 14 years to the day after Venus beat Serena in the 2001 final at Flushing Meadows, they met again with so much at stake.

Well-known folks such as Donald Trump — who was booed when shown on video screens — Oprah Winfrey and Kim Kardashian dotted the teeming stands in Arthur Ashe Stadium, and the sellout crowd of 23,771 got its money's worth.

"They both played their best," said Serena's coach, Patrick Mouratoglou. "If they were feeling uncomfortable with playing each other, they could not play at that level."

The sisters combined for 57 winners (Serena had more, 35) and only 37 unforced errors (Venus had fewer, 15). How close was it? Serena won 76 points, Venus 75.

Both pounded serves fast, very fast, each topping 120 mph. Both returned well, oh so well, each managing to put into play at least one serve at more than 115 mph by the other.

Venus often attempted to end baseline exchanges quickly. Serena showed tremendous touch by using drop shots, one paired with a backhand passing winner, another with a perfectly curled lob.

When a reporter implied he wasn't sure whether Venus really wanted to beat Serena, the reply was drenched with incredulity.

"I tried," Venus replied. "Were you there?"

On Thursday, Serena faces unseeded Robert Vinci of Italy, who reached her first Grand Slam semifinal at age 32 by outlasting Kristina Mladenovic 6-3, 5-7, 6-4.

In the men's quarterfinals, No. 1 Novak Djokovic defeated 18th-seeded Feliciano Lopez of Spain 6-1, 3-6, 6-3, 7-6 (2) in a match that ended at after 1 a.m. Wednesday. Djokovic's semifinal opponent Friday will be defending champion Marin Cilic, who edged 19th-seeded Jo Wilfried-Tsonga 6-4, 6-4, 3-6, 6-7 (3), 6-4.

The 43rd-ranked Vinci is playing in the 44th major tournament of her singles career, the second-most appearances by a woman before reaching her initial semifinal. Vinci is 0-4 against Serena and joked about wearing a helmet for protection from some of the 33-year-old American's booming shots.

"She's the favorite. Maybe she'll feel the pressure. Who knows? It all depends on her. If she serves well, it's tough to return," Vinci said. "But I have nothing to lose."

Against Venus, Serena earned a key break to lead 2-0 in the third set thanks to a down-the-line backhand winner that landed in a corner, then she gritted her teeth, held clenched fists near her head and leaned forward, holding the pose. When she got to match point as a shot by Venus sailed long, Serena dropped to a knee behind the baseline and pumped an arm, her back to her sister.

Serena then smacked a 107 mph ace, her 12th, to end it.

At 35, the oldest woman to enter the tournament, Venus had her own reasons for wanting to beat Serena, of course. She hasn't reached the semifinals at any Grand Slam tournament since the 2010 U.S. Open, and might have considered this her last, best chance to collect an eighth major singles championship of her own.

Mouratoglou was asked whether Venus can do that.

"I think so," he responded, "except if she plays Serena."

Novak Djokovic's U.S. Open quarterfinal was suddenly tied at a set apiece, and he tore off his shirt as he headed to the sideline. He sat, halfheartedly tried to smash his racket, then began screaming.

Hardly the first time, nor likely to be the last, that Djokovic has let out a little emotion during a match. Whatever gets you through the day, right?

Gathering himself after getting pushed around a bit by an opponent with an unconventional style, Djokovic wound up reaching the semifinals at Flushing Meadows for the ninth consecutive year with a 6-1, 3-6, 6-3, 7-6 (2) victory over 18th-seeded Feliciano Lopez that finished a little after 1 a.m. Wednesday.

"It was frustrating at times," the No. 1-ranked Djokovic said, "but this is the quarterfinals of a Grand Slam. This is what you expect."

For all of his success getting to the closing days of the U.S. Open, though, Djokovic has one championship to show for it, in 2011. His other eight major titles came at either the Australian Open or Wimbledon.

Still, Djokovic is certainly consistent: He has now made it to the semifinals at 22 of the past 23 major tournaments.

"I hope I can keep on going," the Serb said.

On Friday, he will take on defending champion Marin Cilic, who was unfazed by wasting a big lead or match points while holding on to beat 19th-seeded Jo-Wilfried Tsonga of France 6-4, 6-4, 3-6, 6-7 (3), 6-4 earlier Tuesday.

"A big mental fight," the Croatian called it, "especially after losing that fourth set."

Djokovic has never lost to Cilic, winning all 13 of their matches.

The two men's quarterfinals on the other half of the men's draw are Wednesday: No. 2 Roger Federer vs. No. 12 Richard Gasquet of France, and No. 5 Stan Wawrinka vs. No. 15 Kevin Anderson of South Africa.

Lopez's loss dropped him to 0-4 in Grand Slam quarterfinals; this was his first time that far in New York.

He is a 33-year-old lefty who is that rare player these days who likes to use serve-and-volley tactics, doing so 41 times against Djokovic, winning the point 28 times. Djokovic, a brilliant baseliner, tried serve-and-volleying twice.

"There were a few moments in which I had the No. 1 player in the world in a tough spot," Lopez said.

His only break of the match came in the second set, and he made it count. Serving out that set, he saved a break point, then ended the game with an ace and pounded his chest. That's when Djokovic was soon in his chair, bare-chested and bellowing.

Yet 40 minutes later, Djokovic was back in control, serving out the second set at love and capping it with a forehand winner.

Cilic appeared to be heading to a relatively straightforward win after taking the first two sets, considering he was 47-0 in his Grand Slam career when up by that margin. But Tsonga took the third set by finally converting his seventh break point of the match, and then serving it out from 15-30 by taking the last three points with a pair of service winners at 131 mph and 132 mph, followed by a 124 mph ace.

Tsonga, the 2008 Australian-Open runner-up, then saved three match points in the fourth set to force a fifth.

"Jo just came up with amazing shots," Cilic said.

In the last set, Cilic broke at love to lead 3-2, and didn't falter this time, although he did need another two match points to close it out, double-faulting on one, before finally winning when Tsonga sailed a forehand long.

"It's a lot of frustration, of course, but that's tennis," Tsonga said.

Tsonga entered his quarterfinal against Cilic having held in all 56 of his service games in the tournament, a streak that reached 60 before Cilic broke to go up 5-4 in the first set. Cilic broke early in the second, too, and wound up winning three of Tsonga's service games.

Tsonga helped out by double-faulting 11 times.

"I just served, I would say, very bad compared to the other days," Tsonga said.

Cilic, meanwhile, hit 29 aces and saved nine of 10 break points.

Cilic wore a thick brace on his right ankle, which he tweaked during his fourth-round victory over another Frenchman, Jeremy Chardy. But it was Tsonga who appeared more troubled by an ailment, wearing a thick band of tape under his left knee.

"I don't really want to talk about this, you know," Tsonga said. "It's part of the game, unfortunately, for me."