ABNアムロ世界テニス・トーナメント
At Rotterdam Open third seeds Kubot and Koolhof defeated Ben McLachlan and Kei Nishikori before losing to Jeremy Chardy and Fabrice Martin in the second round. The pair reached the Masters 1000 quarterfinal at the 2021 Mutua Madrid Open where they were defeated by No. 2 seeds and eventual runners-up Pavić/Mektić.