Novak Djokovic says he will need to be at his very best to see off Andy Murray in their US Open quarter-final clash later on Wednesday.

The two rivals go head to head for the 21st time in the last eight in New York with the Serbian star viewed as the favourite as he looks to end Murray’s 2014 Grand Slam challenge.

Djokovic has won 12 of the 20 matches between the two but Murray (9.00 – US Open) has claimed big victories to beat the current world number when lifting the Flushing Meadows title in 2012 before his famous triumph in the Wimbledon final in 2013.

Djokovic knows he must not underestimate the Scot in Queens later.

“We all know his quality,” he said. “He knows how to play on centre court at the US Open where he has played some great tennis and we’ve had some great matches. It’s a very tough draw. I’m going to have to be playing my highest level in order to advance.

“I think he performs his best in the Grand Slams. He’s been on and off this year but I think in the big matches, as the tournament progresses, he’s still fit. He still plays very high-quality tennis. That’s what I expect him to do.”

Wednesday’s other quarter-final sees third seed Stanislas Wawrinka (13.00 – US Open) take on Kei Nishikori (41.00).