SHANGHAI (AFP) - Rafael Nadal survived a rollercoaster encounter with fourth seed Marin Cilic to power into Sunday's final of the Shanghai Masters and much-anticipated showdown with old rival Roger Federer.

The Spanish world No. 1, who has never won the tournament but is on a terrific run of form, finally saw off the Croat after saving three set points in the opener on the way to a tense 7-5, 7-6 (7/3) victory.

Timeless Federer fought back from a set down to beat Juan Martin del Potro in the later match on Saturday.

The Swiss legend and world No. 2 was uncharacteristically off-touch in meekly losing the first set, but he rolled back the years to defeat the Argentine 16th seed 3-6, 6-3, 6-3.

Cilic had only ever got the better of 16-time Grand Slam winner Nadal once in five previous meetings, but he made him work hard for this latest win.

Nadal said he was just glad to be in the final.

"The way doesn't matter," he said with a smile. "We are at the highest level of our sport so nobody wins easy. "And if you want to compete in the most important events of the year and try to go for the victories, for sure you're going to have tough matches, and today was one of them."

Nadal, pursuing a seventh title this season, put Cilic under immediate pressure in the Croat's first two service games.

But the 29-year-old Cilic, the 2014 US Open champion, eventually settled, only to squander three set points as Nadal hung on grimly. In the next game the 31-year-old Nadal capitalised, breaking Cilic on the way to claiming the first set.

With the crowd firmly in his favour, the Spaniard broke Cilic again in the third game of the second set, only for Cilic to break back for 3-3 when Nadal put his simple volley into the net.

An angry Nadal bashed his racquet twice on his knee.

They exchanged a further break apiece to race into the tie break, before a grateful Nadal pulled away at the last.