Rafael Nadal sensationally set up a dream Australian Open final against Roger Federer with a marathon win over Grigor Dimitrov.

The Spanish 14-time grand slam champion was forced into a titanic battle on Rod Laver Arena before winning 6-3 5-7 7-6 (7-5) 6-7 (4-7) 6-4 in four hours and 56 minutes.

Nadal, so impressive throughout the tournament at Melbourne Park, will face great rival Federer in a major final for the ninth time and first since 2011.

Sunday's final will be the 2009 champion's 21st in grand slams as he eyes his 15th title, which would see him close in on Federer's record of 17.

Nadal had won seven of his previous eight meetings with Dimitrov, but the Bulgarian 15th seed was the victor in their most recent match and pushed his illustrious opponent to the limit on this occasion.

As expected, the ninth seed regularly attacked Dimitrov's one-handed backhand with his top-spin forehand, just as he is likely to do against Federer on Sunday.

But Dimitrov stood firm, admirably sticking with Nadal in what must surely rank as the standout performance of the 25-year-old's career.

Nadal was under threat early but was the first to break, an approaching Dimitrov unable to return a forehand down the line to fall 3-1 behind.

That break was all he would need to take the first set, with Dimitrov struggling against serve after missing his early chances.

Somewhat out of nowhere, Dimitrov broke to love in the fourth game of the second set, during which Nadal was given a time violation by chair umpire Pascal Maria.

A brilliant backhand pass down the line, followed by a Dimitrov double fault, saw Nadal break back in the seventh game.

Sloppiness led to the pair trading breaks again before Nadal saved four set points, two with big serves and another with a forehand winner.

Dimitrov would finally, and deservedly, win the set with his third break of serve, Nadal sending a backhand well long to see the match levelled.

Nadal lifted to start the third set and Dimitrov made back-to-back errors - one from each wing - to fall a break behind.

Uncharacteristically, Nadal failed to consolidate as the baseline exchanges became more gruelling, before both players started to struggle late in the set.

The tie-break was a thriller, but Dimitrov cracked at the decisive moment, sending a forehand wide at 5-5 before Nadal overpowered him, leading to another error to finish the set.

To his credit, Dimitrov hung in there in the fourth to force another breaker, twice holding comfortably when serving to stay in the match.

He carried that form into the tie-break, taking a 5-2 lead before closing out the set to force a decider.

Even as the contest passed the four-hour mark, Nadal again raised the intensity to start the fifth, only for Dimitrov to hold serve after an opening game lasting almost 11 minutes.

The baseline battles continued early in the fifth, Nadal incredibly holding from 15-40 down in the eighth game.

That proved to be decisive as he broke in the next with a backhand winner down the line, on his way to closing out an amazing victory at 00:44 local time.