Santos was acquired to become Toronto's primary closer before the 2012 season, but was injured just three weeks into the season. A similar situation arose the following year when Santos made just a handful of appearances before August.
The hard-throwing right-hander was expected to start this season in an eighth-inning role, but that changed when Janssen suffered an injury during his final scheduled appearance of the spring Friday in Montreal.
"Any time an opportunity is presented to you, you want to make the most of it, and that's all I want to do," said Santos, who recorded 30 saves for the White Sox in 2011. "If I get a couple opportunities at that ninth-inning role, come in, throw strikes and get the job done. Hopefully I can build off that and who knows what could happen."
This opportunity also provides Santos with a shot at redemption following those injury-plagued seasons. In '12 it was a shoulder injury and last year it was a surgical procedure to remove bone spurs from his elbow.
Santos did return in August, though, and allowed just four earned runs over his final 21 1/3 innings. That showed just how dominant he can be, but he admits that he still pitches with a chip on his shoulder because of the checkered past.
"Trust me, for a year and a half just being hurt and being away from anything was one of the most miserable things in the world," Santos said. "That's something that keeps the fire going in me and keeps the fuel going in me. I know where I was then and I know where I want to be, and I'm just going to work as hard as I can and hopefully make the most of whatever opportunity I get."
In Tuesday night's 4-2 victory over the Rays, Santos allowed a run, but stranded runners on second and third by striking out Yunel Escobar looking to end the game.