Serena Williams tops sister Venus in emotional 3-set US Open quarterfinal

No. 1 Serena Williams kept her calendar Grand Slam hopes alive in an electric Arthur Ashe Stadium, beating older sister No. 23 Venus Williams 6-2, 1-6, 6-3 on Tuesday to advance to the US Open semifinals.

Now two wins away from a fifth consecutive Grand Slam title, Serena was asked how special it was to meet Venus at the net for the 27th time.

"She's the toughest player I've played in my life and the best person I know," Serena told Mary Joe Fernandez in the post-match interview. "It's going against your best friend, and for me, going against the greatest competitor in women's tennis."

Related: GIF: Williams sisters embrace at net after Serena wins in 3 sets

Serena improves to 18-1 in three-setters for 2015, with her only loss coming in Toronto against Belinda Bencic - who Venus beat in straight sets Friday. Serena advances to face unseeded Italian Roberta Vinci in the semis, against whom the American holds a 4-0 head-to-head record.

While past meetings between the siblings have been described as "passionless" and even "fixed," Tuesday night was certainly the opposite as the momentum between the champions shifted throughout, leaving the Flushing Meadows crowd in awe.

Venus came out firing with three aces and 11 winners to just five unforced errors in the opening set, but as strong as the elder Williams was, Serena was nearly perfect. The reigning champ began catching her older sister off guard with drop shots, converted a pair of breaks, and took the first set in 33 minutes.

Up 2-1 in the second, the crowd roared as Venus got her first break opportunity of the match, but Serena came back with a big forehand winner to take the game back to deuce. An errant Serena backhand gave her another advantage and the world No. 1 double-faulted for the first time since Round 3, putting Venus up a break.

Venus secured a double-break lead in her sister's next service game to go up 5-1, and held on from there to take the set 6-1. After committing just two unforced errors in the first set, Serena unraveled to hit nine in the second, sending the match into a decider.

The 21-time champ found her form quickly in the final set, firing an ace past Venus to take the opening game and grabbing an early break to go up 2-0. Down 30-40 in the third game, Serena let more emotion show with each point as she fought back for a crucial hold.

Down 2-5, Venus held with an ace to stay alive, setting Serena up with a chance to serve for the match. The younger Williams earned a double match point and converted with her eighth ace of the set to cap an incredible quarterfinal.