Afterward, Janssen called it a step in the right direction, and for the first time in a while, he seemed confident that he'd be good to go next week.
"Opening Day is looking more and more realistic," Janssen said.
Janssen had his doubts about that these past few weeks as he worked to recover from an offseason surgical procedure on his collarbone. He was shut down once to allow the soreness to calm down, and just last week expressed doubts about when he'd be ready to pitch in a regular-season game.
Janssen's availability is even more critical because Sergio Santos, the team's other option, has struggled with his control coming back from the shoulder surgery that ended his 2012 season last April.
All this is important because this is no typical season for the Blue Jays, who had an active offseason and will begin the season as the consensus favorite to win the American League East.
No team improved itself as much as Toronto, with the addition of 627 innings to the starting rotation in Josh Johnson, R.A. Dickey and Mark Buehrle, and two impact bats to the top of the lineup in Jose Reyes and Melky Cabrera.
Only the bullpen is a question mark, because the Blue Jays don't have anyone who has closed games for an entire season. Manager John Gibbons has attempted to calm concerns by saying he's confident in the guys he has and that they'll be healthy when it counts.
Still, Toronto scouts have been looking at potential bullpen help in both Florida and Arizona in case Janssen and Santos aren't ready. If nothing else, Monday was a day that allowed an entire organization to take a deep breath.
"They're all here, and they all seem fine," Gibbons said. "That eliminates a lot of problems. We feel pretty good."
The Blue Jays will evaluate how Janssen feels before deciding when his next appearance will come. He's somewhat unique among Major League closers because he relies more on command than a blazing fastball, so his 89-mph heater shouldn't be a huge concern.
"I'm not going to blow anybody away, so I need to have everything working," Janssen said. "The more I get on the mound, the more I challenge my arm."
Janssen proved last season that what he lacks in velocity, he makes up for with location, movement and fearlessness. He showed it all off on Monday when he entered the game and promptly struck out Phillies outfielder Domonic Brown on a big, knee-buckling curveball.
Janssen then got John Mayberry to take an 89-mph fastball on the corner for the second strikeout and finished the appearance by getting Kevin Frandsen to swing and miss at another big curve.
"Once I got heated up, everything felt good," Janssen said.
His fastball was slightly below last season's velocity, and it's reasonable to assume he might reach 90 mph consistently as he gets stronger.
"I'd love a couple more miles per hour," Janssen said. "But I'm a command guy. I've got to hit my spots. Velocity is secondary, but it's also nice to have a little bit more."
Janssen had appeared in more than 200 Major League games in five-plus seasons last May when he stepped in for Santos and took over the closer duties. He was terrific, making good on 22 of 25 chances. In a sign of Janssen's domination, he only issued 11 walks as opposed to 67 strikeouts.
"I love it. I love the pressure," Janssen said. "I love pitching with the game on the line. Being the last man standing back there in the ninth is fun. I think everybody who pitches in the bullpen aspires to be a closer. I don't think anyone wants to be a middle reliever."
Being the last man standing could be especially fun in a summer when the Blue Jays appear to be headed for a special season. They haven't been to the playoffs in 20 years, and expectations are running high.
"It's an honor, a privilege," Janssen said. "There are plenty of guys we have confidence to do that job. But right now, it's me. I'm going to do it as good as I can."