Stubborn Serena Williams refused to roll over Wednesday against her big sister Venus, saving 10 set points in a heroic struggle before pounding out a 7-6 (8-6), 7-6 (9-7) win to advance to the semi-finals of the US Open. ( dpa )
The fourth seed, who lost to her sibling in the Wimbledon final, made sure that scenario did not repeat itself with an intense victory in well over two hours.
Serena Williams, now 9-8 in the series with her sister, reached the final four in New York for the first time since 2002 when she won the title over her nearest relative.
The younger Williams next faces Russian Olympic silver medallist Dinara Safina, who stopped Italian Flavia Pennetta 6-2, 6-3.
"I think today maybe I can say finally I'm happy with myself, the way I played, because really I did what I had to do," said the sixth-seeded Russian and finalist in six of her past seven events. "I was aggressive on the court."
Serena Williams was overjoyed to have gone through against her sister, always her toughest opponent.
"It felt like a final," the eight-time Grand Slam champion said. "I can't belive I won. It's tough to play against a sister. She was serving well. I just tried to stay with her."
Serena Williams said she kept her eyes off her opponent: "I tried not to look at her. If I did, I might start feeling sorry."
The winner trailed in both tiebreakers. "When I got down I was so relaxed, I just started running a lot of balls down."
"It's unfortunate this had to be in the quarters, but we're both fighting to get our rankings back," the former number one said.
Scot Andy Murray ended the 23-match winning streak of Juan Del Potro, reaching the first major semi-final of his career 7-6 (7-2), 7-6 (7-1), 4-6, 7-5.
"I'm excited to be in the semi-finals, but the tournament is still going," said the sixth seed headed for a ranking of fourth. "I said at the start of the tournament, I want to try to win it."
Murray laboured for nearly four hours in a high-tension shootout with the Argentine teenager who has won titles at his past four tournaments.
Murray began fulfilling his promise as the 2004 junior winner at Flushing Meadows with a winning performance featuring nine aces and 61 unforced errors in the battle of attrition.
"I had a bit of a slip in the third set," the Scot said. "Del Potro's been on an unbelievable run."
The Argentine dropped the first two sets - around one hour each - in tiebreakers, then went on a tear as he won 12 of the 13 last points to claim the third.
He twice went up breaks in the fourth set as Murray clawed them both back before advancing in relief as a return from Del Potro sailed long on a second match point.
Murray faces a semi-final against either top seed Rafael Nadal or American Mardy Fish, whose match started near midnight.