Niemann had to leave the game after one inning when he was hit on the right ankle by an Adam Lind comebacker. Subsequent x-rays revealed a small fracture in his right fibula.
That forced an emergency appearance by Ramos (1-0), who earned his first major league victory with three innings, during which he allowed one run on two hits while overcoming three walks.
Toronto's Brandon Morrow (4-2) absorbed the loss after yielding six runs (five unearned) on four hits over five innings.
The Blue Jays fell for the third time in four games.
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