Serena Williams twice came from behind to complete a nail-biting 7-6 7-6 win over her older sister Venus and claim a place in the U.S. Open semi-finals.
In a match of high quality where no quarter was given, Serena trailed 5-2 in the second set tiebreak before clawing her way back to seal victory in two hour 25 minutes.
Twice champion Serena, the fourth seed, saved eight set points in the second set before seventh-seeded Venus hit a forehand long to surrender the match, losing the tiebreaker 9-7.
Serena, who edged ahead 9-8 in overall meetings between the siblings, will next meet sixth-seeded Russian Dinara Safina for a place in the final.
In the other semi Jelena Jankovic will play Elena Dementieva.
