Defending champ Ben Shelton through to quarterfinals at Montreal

Defending champion Ben Shelton continued his National Bank Open title defense in remarkably strong fashion with a 6-3, 7-6 (3) defeat of Joao Fonseca on Sunday to reach the quarterfinals in Montreal.

Shelton, the fifth-seeded American, and Fonseca, the 22nd-seeded 19-year-old from Brazil, had each not yet dropped a set in the tournament. Shelton was broken in the first game of the match but immediately broke back and then once again up 4-3 to claim the first set.

He then rallied from 3-0 down in the second set to complete the sweep.

The windy conditions in Montreal affected both Shelton and Fonseca, but Shelton (26 winners to 26 unforced errors) managed it far better than Fonseca (15 winners, 32 errors).

"It was tough out there today and I competed well," Shelton said. "It wasn't easy conditions to play in. I struggled to find my footing on a lot of balls, as did he. A lot of it just comes down to grit in a match like this. So to come through with a win against a really high-quality player like Joao is huge for me."

Shelton will face No. 13 seed Jakub Mensik for a spot in the semifinals after the Czech competitor swept the Netherlands' Botic van de Zandschulp 6-4, 7-5 in the final match of the night.

Both Mensik and van de Zandschulp had two double faults but Mensik held a sizable 13-1 edge in aces, won 81% of his first-serve points and converted three of four break-point chances on his opponent's serve, including in the final game of each set.

On the other side of the bracket, young ATP tour pros Learner Tien and Spain's Daniel Merida both won convincing victories and will meet in a Tuesday quarterfinal match.

The 12th-seeded Tien knocked off Argentina's Thiago Agustin Tirante, 6-4, 6-4, while Merida defeated weary Dutchman Tallon Grieskpoor, 6-3, 6-1.

Tien, 20, has earned his second quarterfinal appearance at a Masters 1000 event, having reached the final eight at Indian Wells in March of this year.

Tirante broke Tien in the match's opening game, but the Californian returned the favor in the fourth game. The two remained on serve until an eight-point 10th game, when Tien broke to capture the first set.

Tien, who won on the clay in Geneva in May at an ATP 250 event, served for the match at 5-3, but Tirante broke at love. Undaunted, Tien won the first three points in the following game and closed out his opponent on an unforced error.

The match featured a combined 49 winners, but 67 unforced errors. Tien didn't come to the net often, but did win 11 of 12 points.

"I thought during rallies it was tough because it was really windy today," Tien said. "I felt like the ball was swirling in every rally. I saw the ball well on return."

The rapid-rising Merida, 21, reached his first ATP quarterfinal by relying on an efficient first serve in the win over Griekspoor. The Spaniard won 25 of 30 first serve points over his Dutch rival.

Merida was never broken and delivered 18 winners to only nine unforced errors. Griekspoor committed 29 errors and only recorded 13 winners.

The match only took 69 minutes to complete.

"I feel amazing playing here. I knew I have the level after winning my first title a few weeks ago (at Umag) and I am just aiming to give 100 per cent every point," said Merida. "I try to play solid on my backhand and I think I've always had a good backhand. I try to hit it as much as possible and here it feels really great."

--Field Level Media