Serena Williams overcame sister Venus in a topsy-turvy affair Tuesday night at Flushing Meadows.

Serena emerged victorious in three sets, winning 6-2, 1-6, 6-3, as Venus threatened to put the brakes on Serena’s plan to win the Calendar grand slam.

Serena comfortably won the first set 6-2, but then seemingly switched off as Venus won the second even more comfortably; the 35 year old dropping just one game to win 6-1.

But Serena rallied back to pick up the third set, wrapping up victory in a neat hour and 38 minutes.

Venus Williams has in recent times rarely triumphed over her dominant younger sister, and it was not to be on Authur Ashe court as well.

Serena meets Italian Roberta Vinci in the semi finals on Thursday as she attempts to match Steffi Graff’s 1988 achievement.

Serena has already won the Australian, French, and British Opens in 2015. Winning the US’ on Sunday would give her the Calendar Grand Slam, a unique and historically difficult achievement.