Lynn said he understood, expressed appreciation for the opportunity to start, too. If he felt any pressure, he never did let on. Pressure had always been a part of his upbringing.
At 24 years old, he beat every other Major League pitcher to four wins this season, and he's pitched in more critical spots than many of his big league elders. As a 5-foot-9 12-year-old, Lynn helped lead a team from Brownsburg, Ind., to Williamsport, Pa., where it competed in the 1999 Little League World Series. Lynn pitched and played first base for that club.
As a teenager, he was a cog on a Brownsburg High School team that made three consecutive trips to the state championship. When the team finally won it all in 2005, Lynn was on the mound, capping a season in which he went 16-0 with a 0.71 ERA.
Lynn missed pitching in the College World Series while at Ole Miss by one game but managed to work his way onto a Major League World Series roster before earning a spot on an Opening Day one.
Each represented a stop on the way to a place in a big league rotation.
"When you pitch in those situations growing up, it helps you better adjust to what life is going to be here," Lynn said. "I have those things to fall back on, knowing that I was successful in those big spots before. No situation is too big."
Not even Lynn's current task, the seemingly unenviable one of being asked to step in for a pitcher who has long carried the Cards on his back.
"I think it is part maturity. I think part of it is toughness," Matheny said. "He's tough between the ears and is physically strong, and that adds a confidence to it."
If the Cardinals had unspoken expectations for Lynn, he has certainly exceeded them. He did something Carpenter never has by winning each of his first four starts and posting a 1.33 ERA in April. Lynn has yet to allow more than one run in a start, and he has pitched from behind for only one of his 27 innings.
While Lynn's results will eventually even out, his makeup and ability would suggest that success can be sustained. Much of that is a credit to the way the Cards developed Lynn in the Minors.
The 39th overall pick in the 2008 First-Year Player Draft, Lynn was running on fumes when he joined the organization. He had just pitched 89 1/3 innings for Ole Miss during his junior year and tossed another 26 2/3 when he entered the Cardinals' system. When Lynn arrived at the organization's fall instructional league, he was quickly sent home.
"He was complaining about aches and pains and such," recalled bullpen coach Dyar Miller, who, at the time, was the Cards' Minor League pitching coordinator. "Actually, I was a little concerned about the durability."
Those concerns didn't persist. Lynn did not miss a start over the next two seasons. And the only aches and pains he endured were ones of a pitcher being groomed for long-term success.
The organization, as it routinely does with pitchers, pushed Lynn to complement his four-seam fastball with a two-seam sinker. As he tinkered with various grips in the Minors, Lynn lost velocity. That velocity has since ticked back up, so much so that Lynn is throwing harder now than he ever did as a Minor League starter.
"I was trying to make the ball move and that was taking away from my stuff," Lynn said. "What they helped me realize is that you can still have stuff and move the ball the way you're capable of without holding anything back."
During that development, Lynn also put his mechanics back in sync. That included using more hip movement to improve leverage and momentum toward the plate.
"He's using his body a lot better than when he first signed," Miller said. "And he's staying healthy, too."
That sinker is now one of five pitches in Lynn's repertoire. With three different fastballs -- the cutter is the other -- to go along with two offspeed pitches, Lynn has avoided becoming predictable in his pitch selection. That is also a credit to catcher Yadier Molina, who Lynn implicitly trusts.
Lynn's last start, in particular, was an intriguing test for a pitcher who is just beginning to become known. Facing the Cubs for the second time in two weeks, Lynn combated the adjustments Chicago made to him by making better ones himself.
He pitched a career-high eight innings that day.
"I think [teams] are going to try and continue to do different things as they watch and study," Matheny said. "But it's hard to really put a real good plan together when you're making good quality pitches."
Meandering through the Minors' learning curve, plus a successful stint pitching in the bullpen last season, put Lynn on the precipice of breaking out when given the chance to start.
He has helped stabilize a rotation that is among the league's best even without Carpenter or a win from Adam Wainwright. Lynn has also hushed calls for the Cards to look externally for additional starting pitching help.
While Lynn insists that he does not see this as an opportunity to solidify a rotation spot beyond Carpenter's absence, he's certainly doing so. Not only is Carpenter's long-term status unknown, but the Cardinals could lose both Kyle Lohse and Jake Westbrook to free agency after the year.
"Coming into Spring Training, my only goal was to make the team, even if it was a guy that was carrying the bags," Lynn said. "I wanted to pitch as well as I could. So far, I'm getting the job done. Hopefully I can keep doing this."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.