NEW YORK — If Serena Williams would feel sympathy for any opponent standing in the way of her pursuit of tennis' first true Grand Slam in 27 years, it might very well be her sister Venus.
Still, no way was Serena going to let anyone, or anything, stop her on this night, even if she found herself in a mid-match lull while facing her older sibling in the U.S. Open quarterfinals.
Moving two matches from history, top-seeded Serena got all she could handle from 23rd-seeded Venus before moving into the semifinals at Flushing Meadows with a 6-2, 1-6, 6-3 victory Tuesday in the 27th installment of the unique Williams vs. Williams rivalry.
When it ended, they met at the net for a hug, with a smiling Venus wrapping both arms around Serena.
"She's the toughest player I've ever played in my life and the best person I know," Serenasaid in an on-court interview. "It's going against your best friend and at the same time going against the greatest competitor, for me, in women's tennis."
Serena is 16-11 in their matches, including 9-5 in majors and 3-2 at the U.S. Open. Of greater significance, Serena can still become the first player since Steffi Graf in 1988 to collect all four Grand Slam titles in a calendar year.
And 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.
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 action under the lights often was of high quality.
The sisters combined for 57 winners (Serena had more, 35) and only 37 unforced errors (Venus had fewer, 15).
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.
Serena grabbed the last four games of the first set. But she showed some jitters early in the second, double-faulting to trail 3-1, part of a five-game run for Venus to even the match.
They had played 63 intense minutes, so aware of each other's tactics and tendencies, and now it was going to all come down to one set.
At 35, the oldest woman to enter the tournament, Venus had her own reasons for wanting to win, 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.
True to her word, their mother, Oracene Price, did not attend the match. And neither of her daughters betrayed much in the way of emotion.
When Serena, who is 15 months younger, earned a key break to lead 2-0 in the third thanks to a down-the-line backhand winner that landed in a corner, she gritted her teeth, held clenched fists near her head and leaned forward, holding the pose. She did not shake those fists or scream or jump, the way she usually does against other women.
And when she got to match point as a shot by Venus sailed long, Serena dropped to a knee behind the baseline, her back to her sister.
Serena then smacked a 107 mph ace, her 12th, to end it.
On Thursday, she will play unseeded Robert Vinci of Italy, who moved into the first Grand Slam semifinal of her career at age 32 by outlasting Kristina Mladenovic of France 6-3, 5-7, 6-4.
In the men's quarterfinals, defending champion Marin Cilic let a big lead and match points slip away before holding on in the end to beat 19th-seeded Jo Wilfried-Tsonga of France 6-4, 6-4, 3-6, 6-7 (3), 6-4. No. 1 Novak Djokovic was to face No. 18 Feliciano Lopez of Spain in Tuesday's last match.
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. She is better known for having won a career Grand Slam in doubles with former partner Sara Errani.
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."
The quarterfinals on the other half of the draw are Wednesday: No. 2 Simona Halep of Romania vs. No. 20 Victoria Azarenka of Belarus, and No. 5 Petra Kvitova of the Czech Republic vs. No. 26 Flavia Pennetta of Italy.
Get past Vinci, and Serena would go against one of those four women in the final. Her head-to-head record against each is lopsided: 6-1 against Halep, 17-3 against Azarenka, 5-1 against Kvitova, 7-0 against Pennetta. Worth noting, though: Kvitova is responsible for one ofSerena's only two losses in 55 matches this season, on red clay at Madrid in May.