John Isner and Milos Raonic are serving up some ominous numbers to their Australian Open rivals at Melbourne Park.

The Open smokeys have both blasted their way into the third round without dropping a single game on serve, let alone a set.

Isner, seeded 10th, is looking particularly threatening after downing Spaniard Marcel Granollers 6-3 7-6 (8-6) 7-6 (7-2) on Thursday to book a date on Saturday with Feliciano Lopez.

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“He actually beat me on this court a few years ago,” Isner said of Lopez.

“We have been on tour for eight years together. He’s a big lefty server and likes fast courts. It will be a tough match.”

The American has fired down a tournament-high 57 aces and is yet to face a solitary break point.

Raonic, the 13th seed who opened his season with victory over Roger Federer in the Brisbane International final, is also looking untouchable on serve.

The Canadian took his ace count to 37 in his 7-6 (8-6) 7-6 (7-5) 7-5 victory over Spanish veteran Tommy Robredo.

Raonic next faces Viktor Troicki, who defeated Tim Smyczek 6-4 7-6 (7-5) 7-6 (7-4) on Thursday.

Frenchman Gael Monfils also banked another straight-sets win, two days after the enigmatic 23rd seed’s path to the quarter-finals opened up following the surprise exit of former world No.1 Rafael Nadal and 11th seed Kevin Anderson.

Monfils sent compatriot Nicolas Mahut packing with a 7-5 6-4 6-1 victory and next plays countryman and qualifier Stephane Robert.

The 29-year-old would then have expected to meet Nadal in the fourth round – if the Spanish fifth seed didn’t suffer a shock opening-round loss to Fernando Verdasco.

Verdasco couldn’t back up the boilover, with world No.87 Dudi Sela beating him 4-6 6-3 6-3 7-6 (7-4) on Thursday.

Lopez, Troicki, Joao Sousa and Steve Johnson also advanced to the third round of the Open on day four.

Lopez beat Guido Pella 7-6 (7-2) 6-7 (4-7) 7-6 (7-3) 6-7 (8-10) 6-4, with the clash lasting four and a half hours.

It was the first time a five-set match at the Open has featured four tiebreaks since 1993.

-AAP