Rafael Nadal progressed through to the quarter-finals of the Australian Open with a straight sets victory over Kei Nishikori, but it was a far from comfortable outing for the world number one.

Nadal had won all five of his previous meetings against Nishikori and, while he made it six out of six on Monday, he was pushed hard by his Japanese opponent before sealing a 7-6 (7/3) 7-5 7-6 (7/3) win at Rod Laver Arena.

The 13-time grand slam winner had not been broken previously in the tournament but dropped four of his service games before finally ending the impressive challenge of Nishikori in a match that lasted three hours and 17 minutes.

Nadal looked poised for a straightforward fourth-round outing as he broke Nishikori in the opening game following some loose shots from the world number 17.

The omens were not good for the underdog with Nadal's serve having proved infallible in his opening three matches in Melbourne, but the top seed was finally broken after four uncharacteristic errors in the fourth game.

Suddenly it was the 16th seed who was starting to look the more formidable and Nadal only just managed to hold in his next service game.

The set went with serve to a tiebreak, where Nadal showed his superior experience to emerge a 7/3 winner.

Nadal did not have it any easier in the second set either, and he was broken again in the fifth game after putting an overhead smash wide with the whole court to aim for.

That put Nishikori 3-2 in front but Nadal broke back in the eighth, taking the game with a crunching forehand down the line, and the 2009 champion produced a similar shot to take the set as he broke his opponent's serve again in the 12th.

Nishikori continued to fight in the third but his challenge finally looked to be fading as Nadal took a 4-1 lead after breaking in the fourth.

However, Nishikori still posed a major threat to the 2012 runner-up and, after failing to make the most of several opportunities in previous Nadal service games, he broke back in the seventh following the Spaniard's first double-fault of the match.

Incredibly, Nishikori also broke Nadal at his next opportunity to go 5-4 ahead and have the chance to serve for the set.

He could not capitalise though, wasting a great chance for a set point, and Nadal recovered to take that game and he then made no mistake in the tie-break to seal the match.

Next up for the Spaniard is Grigor Dimitrov, who became the first Bulgarian male to reach a grand slam quarter-final after beating Nadal's countryman Roberto Bautista Agut 6-3 3-6 6-2 6-4.

Andy Murray smashed a racket in a rare display of frustration after being taken to a fourth set before securing his quarter-final spot with a 6-1 6-2 6-7 (6) 6-2 victory over lucky loser Stephane Robert.

After racing through the first two sets in just over an hour, Wimbledon champion Murray blew a couple of match points in the third and was dragged into a tiebreak by the 33-year-old Frenchman, who won it 8-6.              

It was the first set fourth seed Murray had lost in the tournament.

For two sets it was virtually a stroll in the park for the Wimbledon champion Murray.

Of all the possible opponents he could have faced in the fourth round, Stephane Robert was among the most unlikely.

The 119th-ranked Frenchman initially lost in the final round of qualifying but secured a lucky loser spot 10 minutes before meeting Aljaz Bedene after Philipp Kohlschreiber pulled out.

Robert won that one and two more to become the first lucky loser ever to reach the fourth round at Melbourne Park.

But from 1-1 he lost nine straight games, with Murray ending the first set on a run of 11 straight points.

Robert had never previously been beyond the second round of a grand slam event, with his greatest moment prior to this tournament coming when he beat Tomas Berdych at the French Open in 2011.

Murray's purple patch continued until Robert held for 1-4 and, although the Scot had no trouble clinching the set, there were signs things were about to get tougher.

He served double faults on his first two set points, betraying nerves that were perhaps attributable to this being only his sixth competitive match since back surgery.

The start of the third was certainly much closer but Murray looked like he had done the hard work when he forged ahead to lead 4-3, overcoming frustration to take his seventh break point.
That was emphatically not how it turned out, however.

Murray brought up two two match points at 5-4 but missed both, the first with a double fault, and, on his sixth break point, Robert secured his first break of the match.

The engaging Frenchman deserved his reprieve, and he made a flying start to the tie-break by winning two points on Murray's serve to lead 3-0.

The Scot pegged him back and had two more match points but a poor second serve and a missed forehand accounted for those, too.

Murray then netted a forehand to give Robert his first set point and a forehand long handed it to the Frenchman, Murray taking his frustration out by breaking his racquet.

Murray's first dropped set of the tournament appeared more of an inconvenience than anything more threatening, but he still needed a good start to the fourth.

And he got it with a break to love to lead 3-1, Robert rather handing it to him by double-faulting for the sixth time.

The 33-year-old had already called the trainer to have his thigh massaged, and it was an awfully long way back for him.

Murray thought he had taken his fifth match point when Robert's shot was called wide but it was correctly over-ruled.

A sixth arrived straight after, though, and this time he clinched it when the Frenchman netted a forehand.

It took two hours and 21 minutes but Murray was finally though to his 12th major quarter-final in a row at tournaments he has contested.

Robert stayed on court to soak up some deserved applause as a relieved Murray celebrated surviving his first hiccup.

Next up for the Scot is Roger Federer, who gave a vintage display in trouncing Jo-Wilfried Tsonga.

It was the perfect birthday present for Federer's new coach Stefan Edberg, who turned 48 on Sunday, as an aggressive display from the sixth seed saw him power to a 6-3 7-5 6-4 victory.

But if Federer is to win an 18th grand slam title he will have to do it the hard way, with Murray next up and Nadal and Djokovic likely to stand in his way also.

Age appeared finally to be catching up with the great man last season as he endured his worst year in more than a decade, dropping as low as seventh in the rankings and seeing his run of consecutive grand slam quarter-finals ended at 36.

But Federer always insisted his struggles were largely caused by back problems, which he overcame towards the end of the season.

He began this year with a full winter's training behind him and a new, larger-headed racquet, potentially a key weapon in helping him negate the effects of having lost a bit of speed.

Federer had cruised through his first three rounds but he had not played anyone of note, so assessing his form was not easy.

That was certainly not the case against Tsonga, who Federer beat in five sets in the quarter-finals last year.

From the start the Swiss looked sharp, breaking serve in the second game and easily holding throughout the first set.

All the pressure was coming from Federer and, although Tsonga held on until 5-5 in the second set, the 32-year-old was quick to take his chance when it came.

Federer and Edberg have only been working together for a week but the Swede's influence already seemed apparent, with Federer coming to the net 41 times during the match and winning 34 of the points.

The writing seemed on the wall for Tsonga when Federer broke again to lead 2-1, although the Frenchman at least fought back from 0-40 in the seventh game to keep it to one break.

Tsonga had roared in frustration after Federer won the first three points and hit a ball out of Rod Laver Arena in anger.

It certainly worked in his favour, and in the next game he brought up his first break point of the match but netted a return.

Federer, who served superbly for most of the match, hit his first double fault on his first match point but took it on the second with a clinical forehand volley.

The victory took the Swiss only an hour and 52 minutes, while he chalked up 43 winners compared to 21 unforced errors.