After two seasons with Mooren, Keizer switched partners and played with Marrit Leenstra from 2005 to 2007. In the first year of their partnership, the duo did not place higher than 13th in the first ten World Tour events they entered. Seeded 11th at their next tournament, the $200K Montreal Open in August, they upset two top-ten seeds on their way to the semifinals where they lost to Brazil's third-seeded Talita Antunes and Renata Ribeiro, followed by another loss to Brazil's second-seeded Shelda Bede and Adriana Behar in the bronze-medal match. After Montreal, Keizer and Leenstra had top-ten finishes in four of their last five tournaments of 2005. They also competed in their first World Championships in June as the No. 22 seeds, posting three wins and two losses to tie for 17th place. They closed out their first season as teammates ranked 13th in the world.