World No.1 Serena Williams has defeated sister Venus in three sets to move within two victories of completing the first Grand Slam since 1988.

The younger Williams won 6-2 1-6 6-3 in the US Open quarter-finals on Tuesday in front of a celebrity-filled crowd at Arthur Ashe Stadium.

It was her 11th three-set victory at a major this year.

Serena improved to 9-5 against her sister in Grand Slam matches.

Serena was nearly perfect in the first set but tightened up in the second.

She pulled it back together in the third, breaking Venus’ serve right away. Showing the importance of the moment, Serena started celebrating winners with big fist pumps and loud yells of “Come on!”

The 35-year-old Venus kept up her sharp play of the last two rounds, but Serena – as she so often is against everyone – was simply better.

Earlier Italian veteran Roberta Vinci reached her first Grand Slam semi-final at the age of 32, outlasting France’s Kristina Mladenovic 6-3 5-7 6-4.

The world No.43 saw off her 22-year-old opponent, who had never been beyond the third round at a major before this tournament, and struggled with cramping on a steamy afternoon in New York.

Mladenovic rallied from a break down in the second set to force a decider, but had trainers rubbing ice on her legs during changeovers.

At 3-3 in the final set, the two played a 15-minute game with 10 deuces. Mladenovic had six game points she failed to convert.

After her service was broken, the 40th-ranked Frenchwoman asked for a medical timeout to receive more treatment for cramping.

Vinci protested to the chair umpire as Mladenovic had her left thigh wrapped and it is against the rules to request treatment for an existing injury, but the world No.40 she claimed it was a different problem.

It wouldn’t make a difference. Mladenovic repeatedly bent over in discomfort between points, and Vinci won her last two service games to clinch victory after two-and-half hours.