Roddick delivers knockout in bruising Gonzalez clash

 ANDY Roddick went the distance before finally earning a knockout blow in a bruising fourth round encounter with Fernando Gonzalez at the Australian Open.

ENGAGING: Andy Roddick needed to summon all his fighting instincts to beat Fernando Gonzalez at the Australian Open (Getty Images)

Tempers frequently boiled over in this entertaining baseline slug fest, in which neither player was prepared to given an inch.

But Roddick's experience and calmness under pressure proved decisive as he set up a quarter-final date with Marin Cilic, after securing a 6-3, 3-6, 4-6, 7-5, 6-2 victory.

Number seven seed Roddick raced into an early lead but Gonzalez - beaten by Roger Federer in the final here three years ago - stormed back to claim the next two sets with a series of thumping forehands, which the American failed to read or react to.

Born-fighter Roddick rallied but squandered four set points to force a decider before snatching his fifth attempt in controversial style.

His crunching forehand was initially called out but was overturned on appeal.  Gonzalez was furious and claimed the point should be replayed, insisting he was in place to return.

And that anger seemed to fester at the start of the decider, Roddick securing a decisive early break as the Chilean hurled his racquet to the floor, earning a warning for his conduct.

Meanwhile, US Open champion Juan Martin Del Potro insisted there were 'no excuses' after the number four seed became the highest profile men's casualty, as he was defeated 5-7, 6-4, 7-5, 6-3 in a marathon contest with Croatia's in-form Cilic.

Del Potro arrived in Melbourne carrying a wrist injury and will seek medical advice about treatment before he continues with his ATP Tour schedule.

But he acknowledged that Cilic, who is set for a second consecutive appearance in a Grand Slam last eight, was the better player.

"He's playing great and he just did better than me," said Del Potro, following an exhausting four hour and 38 minute encounter.

"I had chances but he just played too well. In the end I think the serve was my downfall."

Del Potro also admitted he struggled with fatigue during the encounter, calling the trainer onto the court to receive treatment on his left foot.