Victoria Azarenka has said Serena Williams is a player who ‘pushes her to the limit’ as she looks ahead to their US Open semi-final clash. 

The former world No 1 has sealed her spot in the semi-final of a major tournament for the first since 2013 after beating Elise Mertens 6-1 6-0.

Azarenka, 31, who is currently world No 27, said: "I love playing against Serena. We always played on big stages. There were a lot of big fights. 

"She’s one of the players who push me to the limit, who makes me better. I’m excited for that.

“I like playing against the best. That’s where you see yourself, your level, the biggest challenge.”

The Belarusian star has played 23-time grand slam champion Williams 22 times on tour following their first clash in the third round of the 2008 Australian Open.

She added: "That’s what I’m working hard for, to play on the biggest stages against the best players. There’s no one as tough mentally as Serena. I love that challenge.

“I always know one thing: the match is never over. I think the same goes on the other side. No matter what the score is, the match is never going to be over. I think that’s the most visible lesson that we can learn.”

Azarenka will take on the world No 8 later today.