Defending Canadian Open champion Ben Shelton came through another stern test on Sunday, beating Joao Fonseca 6-3 7-6 (7-3) to reach the quarter-finals.

Shelton is the highest remaining seed at the Montreal event, following a swathe of withdrawals and early exits for some of tennis' biggest names, including Jannik Sinner, Carlos Alcaraz, Novak Djokovic and Alexander Zverev.

Nineteen-year-old breakout star Fonseca was viewed as one of the tougher obstacles remaining in Shelton's path, but after his one-hour, 48-minute victory, the American has still not dropped a set this week.

Shelton had found himself trailing 3-0 in the second set, only for Fonseca's movement to be temporarily affected when he went over on his right ankle, allowing him back in.

The Brazilian kept fighting until the last, but Shelton was in front for the duration of the second-set tie-break and will now face Jakub Mensik for a semi-final place.

Mensik beat Botic van de Zandschulp, who had eliminated Daniil Medvedev earlier in the tournament, 6-4 7-5, with a glorious lob on match point getting the Czech over the line.

Along with Shelton and Brandon Nakashima, Learner Tien will be the third American representative in the last eight, having overcome Argentina's Thiago Tirante 6-4 6-4.

Tien will face first-time ATP Masters 1000 quarter-finalist Daniel Merida, who beat Tallon Griekspoor 6-3 6-1 in one hour and nine minutes.

Quarter-finals 

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Young guns rule Canadian Open

Shelton is now into his seventh quarter-final at ATP 1000 Masters level, and all of those have come on hard courts.

He is the first player to reach each of his first seven quarter-finals in the format on hard courts since Kevin Anderson in 2016.

And Mensik's later victory over Van de Zandschulp ensured this year's Canadian Open will make history.

It is the first ATP Masters 1000 tournament where all eight quarter-finalists have been born since the year 2000, with Rafael Jodar, Arthur Fils and Luciano Darderi also in the mix.