Brilliant Murray serves a warning to title rivals

"I have pretty much qualified for the Masters Cup, which was my goal at the start of the year. Hopefully, I can keep the run going in the next round and try to go as far as possible here.

"Once you start to get to the final of Slams, that's when it changes. You have the potential to make history and go down as a great player. The last Slam quarter-final I played, at Wimbledon, I got killed and Nadal played way too good for me. However, I feel like I'm playing much better now." There have been some outstanding floodlight matches in front of the passionate New York fans, but Murray's was not one of them.

The fans became so bored with Wawrinka's mistakes that they started a tedious Mexican wave only four games into the second set.

The umpire had to ask the crowd to stop and advised them to wait until a break in play before finding something to keep themselves occupied high up in the cheap seats. Murray was an innocent party in all of this, playing with quality and class throughout, but half the crowd had headed for home by the time he took the second of his match points after one hour 50 minutes.

At least enough noise was made by those remaining to let the Briton know he had done a good job.

Now comes that difficult match with 17th seed Del Potro, who became the first teenager to make the quarterfinals for seven years by beating Japan's Ken Nishikori 6-3, 6-4, 6-3.

Del Potro should give Murray a far more serious contest than Wawrinka, but the Scot is favourite to line up against Nadal in the semi-finals, provided the Spaniard sees off American Mardy Fish.

The women's event has only two previous Grand Slam winners in the last eight - the Williams sisters - and they have to face each other.

Serena and Venus clash tomorrow and, as Serena, said: "It sucks that it's not the final."

Serena beat Severine Bremond 6-2, 6-2 and Venus took care of Agnieszka Radwanska 6-1, 6-3.

Jamie Murray has reached the quarterfinals of the mixed doubles with Liezel Huber.