Elise Amendola, Associated Press
Serena Williams celebrates a point during the tiebreaker on her way to winning over her sister Venus.

NEW YORK — So little to separate them over their careers, so little to separate them on this night.

Serena Williams barely got the better of older sister Venus Williams in a U.S. Open quarterfinal that was fit for a final, coming back in each set to win 7-6 (6), 7-6 (7) Wednesday night and break a tie in their head-to-head series.

Serena trailed 5-3 in both sets. She faced set points in both, including eight in the second. But she advanced to the semifinals at Flushing Meadows for the first time since 2002, the year she beat Venus in the title match for her second U.S. Open championship.

It was the siblings' 17th meeting as professionals, and Serena leads

9-8. That includes 11 matches at Grand Slam tournaments, where Serena leads 6-5.

She also has the edge in major championships, 8-7, and only she can add to that total this weekend.

"It's really just unfortunate it had to be in the quarters," Serena said.

In the semifinals, the fourth-seeded Serena will meet No. 6 Dinara Safina, who advanced earlier in the day by overpowering No. 16 Flavia Pennetta 6-2, 6-3. No. 2 Jelena Jankovic will face No. 5 Elena Dementieva in Friday's other semifinal.

Tough to imagine either of those contests could come close to producing the quality or competition managed Wednesday by a couple of sisters who grew up honing their strokes on the same court in Compton, Calif. Both played brilliantly, smacking serves upwards of 115 mph, hitting groundstrokes and volleys that would be the envy of nearly every other woman on tour, chasing down balls with "You thought that was a winner?!" defense.

"If it was someone else," Venus said, "I definitely feel like I would have won the match."

In the end, they were separated by three total points, 101-98. Venus had an 8-7 edge in aces. Both double-faulted five times. Both broke serve twice.

The seventh-seeded Venus had all sorts of chances to take control, but in the end, as both women's play reached a very high level, it was Serena who pulled through. In the second tiebreaker, Venus had four set points — and Serena saved them all.

"I'm a very good closer," Venus said, "so today was, um — I've never had a match like this in my life, so I guess there's always a first."

In contrast, when Serena earned her first match point, nearly 2 1/2 hours into the match, she converted it, when the Venus ended an 11-stroke exchange by missing a forehand.

Back when they were ranked Nos. 1 and 2, the siblings only could meet in tournament finals. But because of injuries, inactivity and inconsistency, they dropped in the rankings, and now it's the luck of the draw that determines at which stage they potentially meet.

At Wimbledon in July, for example, the wound up on opposite halves of the field, and Venus beat Serena in the final for her fifth title at the All England Club. At the U.S. Open, they wound up in the same section of the bracket, so the women many consider the two top players at the moment were forced to meet in the round of eight.

The start of the latest all-Williams showdown was delayed by more than an hour because of two lengthy matches that preceded it on the tournament's main court, including a women's doubles match and No. 6 Andy Murray's four-set victory over No. 17 Juan Martin del Potro in the men's quarterfinals. The long day was capped by No. 1 Rafael Nadal against unseeded American Mardy Fish, a quarterfinal that didn't even start until 11:30 p.m.

Venus showed up at the locker room about 20 minutes before she and her sister finally headed out, carrying a bunch of rackets in the crook of her left arm. Serena arrived about five minutes later, a red purse slung over her left shoulder.

Neither face betrayed the slightest hint of emotion, and those same expressionless masks were in place at the match's start. Early on, there were the sorts of nerves and erratic play — a combined seven first-set double-faults, for example — that have marked many of the siblings' encounters as they have adjusted to playing one another.

"I try not to look at her, because if I look at her, I might start feeling sorry," Serena told the crowd afterward. "I want the best for her. I love her so much. She's my best friend."

Neither of their parents, who also serve as their coaches, were sitting in the guest boxes at Arthur Ashe Stadium. An older sister, Isha Price, was there, sitting with her hands clasped in front of her face, eyes shut, during the first-set tiebreaker.

How could she possibly cheer for one sister against another?

"I was stressed," she said. "It is so difficult to watch them. At the end of the day, you want them to play a good match and for the best person to win."

And did the best person win?

"I'm not sure," Price said.

The 23,763 spectators sitting in the packed stands had a hard time figuring out which Williams to support, too. When Venus missed a backhand wide on the match's first point, there wasn't a sound out there — no applause, no yelling, no booing. Nothing.

There wasn't much to separate the sisters' strokes on this night, either.

Down 6-4 in the opening tiebreaker, Serena reeled off four points in a row. That run began when Serena hit a big, cross-court return off an 80 mph second serve, and Venus skidded, then winced, as she chased the ball and dumped her own forehand into the net.

That made it 6-5 for Venus, but Serena erased her sister's second set point with a 107 mph ace. A backhand volley winner set up by a 111 mph serve gave Serena her own set point, and she converted it when Venus pulled a forehand wide after a 10-stroke exchange.

Serena pumped a fist and yelled — exactly the way she would against any other opponent.

Early in the second set, Serena averted more trouble. She began each of her first two service games by falling behind love-30, even facing a break point the second time, but held both times. Venus moved ahead the next time Serena served, though, hitting a winner to go up 4-2.

Serena then held two break points in the next game, but Venus saved them, including with a 121 mph serve.

Take that, little sister!

It wasn't easy for either anytime during the match, and Serena saved three more set points as Venus served for the second set at 5-3, and a fourth when Serena served while down 6-5.

Then came the second tiebreaker, which featured the point of the match. Serena tried a forehand passing shot but Venus stretched and put a volley into a corner. Serena got to that and flicked up a lob that wasn't good enough to get over the 6-foot-1 Venus, who pounded an overhead smash. Now the point was over, right? Nope. Serena got to that, too, stretching the exchange until Venus finally put away a volley to go ahead 5-2.

Fans rose for a standing ovation.

Serena was left gasping for air.

Venus wouldn't allow herself to smile.

Soon after, Venus was ahead 6-3, but Serena won six of the last seven points.

"When I got down, I got so relaxed," Serena said, "and then I started running a lot of balls down."