The 18-year-old Shapovalov, who needed a wild card to get into the tournament, continued his giant killing form at the hardcourt tournament by rallying to beat Nadal 3-6, 6-4, 7-6 (4) on Thursday.
Shapovalov advanced to a quarter-final meeting with France's Adrian Mannarino, who defeated Hyeon Chung 6-3 6-3.
He claimed that he was too passive during those points, and was just plainly "waiting for his shot" and not going for the shots, allowing Shapovalov to be aggressive and overpower him. He aced it by downing the Argentine star 6-4, 7-6 (4), a win that gave him a lot of confidence ahead of Thursday's dream meeting with Nadal.
Wildcard Shapovalov, last year's Wimbledon boys champion, came from a set down to beat the Spaniard 3-6, 6-4, 7-6 at the Uniprix Stadium. He closed out the match with a forehand victor down the line and celebrated by falling onto his back and covering his face with his hands before kissing the Montreal court.
IT was a set of first-serve, first-strike tennis as Nadal won all 11 of his first-serve points, permitting just four points on serve.
The teenager's quixotic bid looked doomed in the third set tiebreaker when he fell 3-0 behind but the world number 143 refused to buckle and only coughed up one more point in the decider. Federer said if it's a two-way race between Rafa and him and he hopes to be him as it means a lot of him to get back at No 1. Whereas, just a weeks later at Indian Wells, Federer said that ranking is not his priority.
"Even though I lost, this is one of the most memorable experiences of my life along with the match I played against him in Toronto", Polansky said.
The Spaniard took a 3-1 lead but found himself at 3-3 after a double-fault.
Federer will face Spain's David Ferrer in the third round.
Polansky earned a stay of execution after holding serve in the sixth game to make it 5-1, but Federer raced into the next round with a comfortable hold, finishing with an emphatic overhead smash.
An early break in the decider put Federer in control as a tired Ferrer began to tire and a characteristically deft volley clinched the match.
Some vintage play at the net helped put Federer 4-2 up with Ferrer seemingly unable to summon a response. Helped by a brilliant return of service, Federer recovered the break in the fifth game and managed to protect for the closure of the set after 35 minutes thanks to a superb forehand in parallel.
Bautista Agut next faces a quarterfinal with Federer, who is preparing for a battle.