Watch: Canadian teen Denis Shapovalov stuns top seed Rafael Nadal at Montreal Masters

Montreal: Canadian teenager Denis Shapovalov shocked top seeded Rafael Nadal to reach the quarter-finals of the ATP Montreal Masters tournament, spoiling the Spaniard's chances of returning to world number one.

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 in three sets, 3-6, 6-4, 7-6 (7/4) on Thursday.

Nadal would have returned to No. 1 in the world if he had defeated Shapovalov Thursday, and then Chung Hyeon or Adrian Mannarino on Friday.

Shapovalov's stunning upset against the reigning French Open champion came as a result of some inspired tennis in front of a boisterous home crowd who cheered his every shot.

Shapovalov had just three wins this season coming into the tournament. He quickly got on a roll in Montreal beating Brazil's Rogerio Dutra Silva in the opening round 4-6, 7-6 (10/8), 6-4. He defeated former US Open winner Juan Martin Del Potro in the second round in straight sets 6-3 7-6 (7/4) to set up the showdown with Nadal.

Shapovalov won seven of the final eight points of the third set tiebreaker before closing out the match with a forehand winner down the line. He celebrated by falling onto his back then covering his face with his hands.

Shapovalov blasted a total of nine aces, including ones on his second serve that handcuffed Nadal. He also had seven double faults and won 67 percent of his first serve points.

Nadal won 77 percent of his first serve points but had just two aces and six double faults in the two hour, 45 minute center court match. Elsewhere on Thursday, Roger Federer maintained his career-long winning streak over David Ferrer to advance to the quarter-finals after a three-set battle with the veteran Spaniard.

Federer, 36, had never lost in 16 previous meetings with the 35-year-old Ferrer, whom he first defeated 14 years ago at the Vienna Indoor tournament. But while Ferrer managed to take the opening set -- ending Federer's 32-set streak -- the Swiss ace raised his game to win 4-6, 6-4, 6-2.

"I actually feel really happy because I know I can play a lot better. David can play a lot better, too," Federer said. "We battled, both tried to find a way to win. You know, he had a good start, I had a better finish."

A strangely error-prone Federer was unable to generate his usual fluency early on, and quickly found himself giving away early breaks to trail 4-1 in the first set. Nowhere was Federer's wayward performance better illustrated than in the seventh game, when he squandered three break points at 0-40 to allow Ferrer to take a 5-2 lead.

Federer held for 5-3 and looked to have clawed his way back into the set with a break of Ferrer's serve in the next game to make it 5-4.

But Federer was struggling again as he served to level the set, finding himself a set point down. He saved the first with an ace but Ferrer made no mistake with his second set point, converting to take the opener 6-4.

Federer responded quickly in the second set, going a break up to lead 3-2 before holding for a 4-2 lead. With Federer slowly improving his first serve, Ferrer was unable to carve out the break opportunities he had found in the first set.

The set went with serve as Federer leveled. An early break in the decider put him in control as a weary Ferrer began to tire. Some vintage play at the net helped put Federer 4-2 up with Ferrer seemingly unable to summon a response.

The decisive break came in the seventh game, with Ferrer netting a forehand return to leave Federer 5-2 up and serving for the match.

Federer promptly went in for the kill, attacking the net and opening up the court to clinch victory with a deft volley.

Federer will now play another Spaniard, Roberto Bautista Agut, in the quarter-finals. Bautista Agut defeated France's Gael Monfils in a gruelling slugfest, winning 4-6, 7-6 (7/5), 7-6 (7/2)."I hope that this match gives me some better rhythm and confidence against Bautista Agut, who plays actually very similar to David," Federer said.