MONTREAL – Defending champion Ben Shelton kept a clean slate at the ATP Montreal Masters on Aug 9, holding off a challenge from Joao Fonseca to power 6-3, 7-6 (7/3) into the quarter-finals.

World number 10 Shelton has not dropped a set in reaching the last eight. The 23-year-old American left-hander will face the winner of a later match between Botic Van De Zandschulp and 13th seed Jakub Mensik.

Brazilian teenager Fonseca, billed as one of the faces for the future of the sport, might have compromised his own chances when he landed badly on his ankle after missing a smash while leading 3-1, 40-30 in the second set.

The youngster was plagued by 32 unforced errors as his opponent mastered an annoying evening wind to earn the victory.

“It was tough today, not easy conditions,” Shelton said.

“With the wind I struggled to find footing on a lot of balls.

“It all came down to grit. The tennis was not clean. Beating a high-quality player like that is huge for me.”

Shelton secured his ninth straight victory in Canada on the second of four match points as Fonseca hit the net with a return after leading in both sets.

Daniel Merida smothered Tallon Griekspoor 6-3, 6-1 as the Spaniard continued his rapid adjustment to hardcourt tennis in Canada.

The world number 63 joins compatriot Rafael Jodar in the Canada quarter-finals and will break through to a career-best spot inside the top 50 as a result of his fourth-round victory.

Prior to making his Montreal debut, clay-courter Merida had never won a tour-level match on hard court.

He will try to extend his streak of cement success to five in a row when he plays a first Masters quarter-final against US 12th seed Learner Tien, who wore down Argentine Thiago Tirante 6-4, 6-4.

Tien saved the first eight break points he faced in the second set in a battle of big ...