New York, Sep 9 (IANS): Top seeds Novak Djokovic and Serena Williams advanced to the semi-finals of the US Open at the Flushing Meadows here.

Serena on Tuesday won an emotional quarter-final 6-2, 1-6, 6-3 against her elder sister Venus and stayed alive in her quest for history -- chasing for a 2015 grand slam title sweep, reports Xinhua.

Serena was facing her 35-year-old sister Venus for the 27th time, and has won 16 of the meetings; she has taken victory in seven of their last eight.

With the game tied 1-1 at the end of two sets, Serena broke Venus' serve early in the third set to take a 2-0 lead, and then went on to clinch the set 6-3 and with it, the match.

Serena converted three of the six break point opportunities to Venus' two of five, and struck 12 aces and committed five double faults to her sister's eight and one respectively.

Serena also hit 35 winners and 22 unforced errors to Venus' 24 and 15 respectively.

When it ended, they met at the net for a hug, with a smiling Venus wrapping both arms around Serena.

"She's the toughest player I've ever played in my life and the best person I know," Serena said in an on-court interview. "It's going against your best friend and at the same time going against the greatest competitor, for me, in women's tennis."

Serena has a chance to win all four Majors in the same season if she can lift a fourth straight title at Flushing Meadows on Saturday. The last to complete the feat was Steffi Graf in 1988.

The 33-year-old American, with 21 Grand Slam singles titles, could also level on Graf's career total if she wins a seventh Open trophy.

The American next plays Roberta Vinci, heading into that semi-final with a 4-0 record against the Italian including a win last month in Toronto.

Unseeded Vinci advanced 6-3, 5-7, 6-4 over Kristina Mladenovic of France.

The 32-year-old Italian showed better fitness over two-and-a-half hours than her French opponent, a decade younger.

Djokovic defeated Spain's Feliciano Lopez 6-1, 3-6, 6-3, 7-6(7-2) with a perfect tiebreak to end the contest.

"Semi-finals of a grand slam is a great achievement and I hope to keep going," said Djokovic.

"I played very consistent, it was just good to go through in four sets."

Djokovic will face holder Marin Cilic, who took a 6-4, 6-4, 3-6, 6-7 (3-7), 6-4 win after four grinding hours against Jo-Wilfried Tsonga.

"I was thinking about third and fourth sets. I didn't play poorly, Jo came up with amazing shots in the critical points, especially on all three match points where he played great points," said Cilic.

"I stuck with my plan and stayed mentally tough and was very difficult day -- very demanding, very, very hot, and of course a lot on the line for the match," he added.