By Alasdair Fotheringham

ALPE DI PAMPEAGO, Italy (Reuters) - Former mountain biker Ryder Hesjedal took a big step towards becoming Canada's first winner of a Grand Tour on Friday when he cut Giro d'Italia leader Joaquim Rodriguez's overall advantage to 17 seconds.

Grimacing with pain as he pulled free of his rivals on the relentlessly steep final, 7.7-km ascent of Alpe di Pampeago, Hesjedal, 31, finished 19 seconds down on lone winner Ronan Kreuziger of the Czech Republic with Rodriguez third, at 32 seconds.

"This was the day the other contenders were supposed to drop Ryder, and Ryder ended up dropping us," Spaniard Rodriguez reflected to reporters with a rueful grin after the arduous, 198-km mountain stage.

"This really changes everything. It's going to be really difficult. He was already probably going to gain time on Sunday's time-trial stage, now he's shown he's really strong in the mountains, too.

"Winning the Giro is in his hands now. But I've got the lead, I'm still there. If you never play the lottery, you'll never win a prize."

While Kreuziger took his first Giro stage win by attacking on the fourth of five classified climbs, Hesjedal's late attack, 1.5 kms from the finish, was enough to go clear of all the other big contenders and score a major psychological blow on his rivals.

Italian Michele Scarponi's lone pursuit of the Canadian allowed him to leapfrog double Giro winner Ivan Basso into third place, one minute 39 seconds back.

"They tried to dislodge me but I showed them my abilities," Garmin-Barracuda rider Hesjedal told reporters. "It's a big day, I'm comfortable with my condition: better 17 seconds than 30."

Asked about his chances on Saturday's even tougher mountain stage, which ends with ascents of the infamous Mortirolo and Stelvio climbs, Hesjedal said: "It will be another epic day in the mountains, more of the same, and everyone will leave everything they have on the road."

Stage winner Kreuziger said his victory on one of the Giro's toughest days in the mountains was a consolation prize after he suffered badly and lost all chance of an overall win on Wednesday's trek through the Dolomites.

"My morale was at zero after Wednesday and I had a hard time getting over what happened," Kreuziger said.

"On the other hand, if I hadn't lost so much time then, there's no way the other contenders would have let me go for the win today."

After Saturday's second straight high-mountain stage, the Giro finishes on Sunday with an individual time trial through the streets of Milan.

(Editing by Clare Fallon)