Only one all-seeded showdown is on Sunday’s fourth-round schedule at the Montreal Masters, but it’s a big one: Ben Shelton vs. Joao Fonseca. Jakub Mensik and Botic van de Zandschulp also have their eyes on the quarterfinals.
(22) Joao Fonseca vs. (5) Ben Shelton
Shelton and Fonseca will be going head-to-head for the second time in their careers and for the second time this season when they meet in round four of the National Bank Open on Sunday. Their only previous encounter came on the red clay of Munich a few months ago, when Shelton prevailed 6-3, 3-6, 6-3 in the quarterfinals on his way to the title.

Fonseca wrapped up his clay-court swing with a quarterfinal run at Roland Garros, but he had not done much since that result prior to arriving in Montreal. However, some time off has certainly done the 19-year-old some good — which is not surprising for someone who has dealt with some physical problems in the early stages of his career. Fonseca is flying high this fortnight with straight-set victories over Stefanos Tsitsipas and Casper Ruud. Shelton, who lifted the trophy in Toronto last year, cruised past Jenson Brooksby and Zizou Bergs to reach the last 16. Somewhat surprisingly, though, the 10th-ranked American has mostly underwhelmed at Masters 1000s and Grand Slams in 2026. This is a nice opportunity for Fonseca to pull off a minor upset.

Pick: Fonseca in 3

Botic van de Zandschulp vs. (13) Jakub Mensik
Mensik is one of only three Masters 1000 champions remaining in the draw (along with Shelton and Cameron Norrie), having triumphed in Miami last season. The 17th-ranked Czech continues to play well in 2026, with a 27-13 record that features a title in Auckland and a semifinal run at Roland Garros. Mensik has advanced this fortnight with defeats of Jake Fearnley and Terence Atmane.

Up next for the 20-year-old on Sunday is a first-ever meeting with Van de Zandschulp, who took thee scenic route into the last 16. The 70th-ranked Dutchman beat Giovanni Mpetshi Perricard in three sets, survived a match against Daniil Medvedev that had 10 service breaks in two sets, and came back from a set, 5-4, and 40-15 down against Hubert Hurkacz to prevail 3-6, 7-6(4), 7-5. It is fair to say that Van de Zandschulp has gotten some help from his opponents in Montreal; an in-form Mensik probably won’t be so generous.

Pick: Mensik in 2