It's just another first for the young right-hander, who joined St. Louis' postseason roster on Tuesday after the club shut down starter Jaime Garcia with a left rotator cuff strain and inflammation.
"It's nerve-racking right now to think about it," Miller said. "Right now, it's gonna be a tough spot for me, as far as what I'm going to do. You never really know out of the 'pen. I'm just looking forward to the opportunity. I'm really excited about it."
With Garcia out of the rotation, Lance Lynn would likely slide back in, though he threw 50 pitches on Monday and probably wouldn't be available unless the Cardinals advance past the NLDS. Miller, 1-0 with a 1.32 ERA in 13 1/2 innings this season, now gives the club another long man out of the bullpen.
"With this roster against the Nationals, we felt like we have more of a need with potentially a pitcher that could go a long ways, especially after we just took Lance Lynn out by him throwing the amount pitches that he threw yesterday," Cardinals manager Mike Matheny said. "We would need multiple innings, and we would need a guy who has worked up to that, and that would be Shelby at this time."
Miller, ranked by MLB.com as the Cardinals' No. 2 prospect, made his debut on Sept. 5 out of the bullpen in St. Louis' 6-2 loss to the Mets. His last outing of the season, on Oct. 3 against the Reds, was his only start. He tossed six innings of one-hit ball, taking a no-hitter into the sixth. But he was left off the initial postseason roster.
"It's my first time up here in the big leagues," Miller said. "Obviously, when I didn't make the roster, traveling with the team, maybe there was a possibility I'd pitch, but the odds weren't great. So it's crazy that I'm on it now. It's definitely going to be a lot of fun. Hopefully I get in there and pitch and help the team win."
Miller has not faced the Nationals this season, but did pitch against Washington in two Spring Training starts. In 4 1/3 innings, he allowed four earned runs on six hits, including two home runs, for an 8.31 ERA.
"We've got all the guys, all the film, and all the veteran guys have been around," Miller said. "We've got [Yadier Molina] catching, and the main thing for me is to just follow him. He knows the hitters real well, he's been around the game for a long time, so I just follow whatever he calls. Even if it's a pitch I'm not comfortable with, I'm gonna throw it. I trust him 100 percent."