Caleb Thielbar thrived in parts of two seasons in the Tigers' organization as he attempted his big league comeback from 2018-19 -- but he never got the call. Back in a Twins uniform now, the 34-year-old left-hander spent Tuesday showing Detroit what it missed out on.

Thielbar struck out five in a scoreless two-inning season debut in the Twins' 4-3 loss, showing off improved fastball velocity and increased confidence in a slider that he feels will be a significant weapon for him this season.

"I feel like everything is syncing up," Thielbar said. "When you’re going good, it just feels like it’s jumping out of your hand rather than just throwing it, I guess. That would be the way I would describe it."

Thielbar had already been one of the surprise stories of 2020, when he made it back to the big leagues for the first time since '15 following a circuitous journey that took him through independent league ball, a collegiate coaching job and thoughts of giving up his playing career after the Tigers and Braves didn't give him a shot to prove himself in the big leagues.

Instead, Thielbar accepted a Minor League deal with his hometown Twins, with whom he'd pitched from 2013-15. He worked his way back to an August callup and posted a 2.25 ERA in 17 games to play himself into the team's continued bullpen plans.

Thielbar feels that this version of himself will be even better. Much of his improvement starts with the slider, which he'd workshopped to add more horizontal movement in the past but couldn't throw consistently for strikes. Thielbar said he has reined in the movement to make it a pitch he trusts much more as part of his game plan alongside his fastball and the slow, looping curveball he has thrown throughout his career.

Thielbar threw the slider 10 times on Tuesday, second most in any outing since he returned to the Twins last season.

"I feel like I can actually throw [the slider] for a strike this year," Thielbar said. "Last year, it was a little bit too big. This year, I’m throwing it a little harder and with a little less break. It still has good horizontal break, but it’s not so big where I’m having trouble finding the zone with it anymore."

Thielbar's fastball also looks to be in good shape to open the season. He topped out at 94.1 mph on a strikeout of JaCoby Jones, marking his hardest pitch since 2014 -- during his first stint in the big leagues.

"He's never really stopped making adjustments, never really stopped working," Twins manager Rocco Baldelli said. "As a guy that's maybe a little older or in some ways, he's a little bit kind of veteran, a guy who's gone through everything he's gone through. What you do see from him though is him continually working and not being satisfied with anything he's doing."

Rooker to IL; Waddell selected
Brent Rooker just can't catch a break, it seems.

Rooker's stint in the big leagues was cut short after a handful of days for a second straight season as he went on the 10-day IL with a cervical strain on Wednesday. The Twins selected the contract of left-handed pitcher Brandon Waddell in a corresponding move and placed Edwar Colina on the 60-day IL with right elbow inflammation to make room on the 40-man roster.

The 26-year-old Rooker wasn't on the Twins' Opening Day roster, but he was recalled following Josh Donaldson's right hamstring injury on Opening Day and went 1-for-11 with six strikeouts in three games. Baldelli thinks that Rooker sustained the strain during a diving catch in left field on Monday.

"Rook was not going to be available today, and we knew that he was not feeling good at all," Baldelli said. "On top of that, our bullpen [had] a few guys being used lately, a few guys that we wanted to stay away from. We had to, I think, get ahead of it if we needed to cover some innings today."

Rooker, the No. 12 prospect in the organization, fractured his right arm on a hit-by-pitch last September and only played in seven big league games last season.

With the Twins no longer playing at a National League stadium this series, the club shortened its bench and added a 14th pitcher by calling up Waddell, who made two MLB appearances for Pittsburgh last season before Minnesota claimed him off waivers.

Waddell was one of the final cuts in Spring Training after he collected 15 strikeouts in 9 1/3 innings with the help of sharply increased slider usage and by working on what the Twins described as the "lowest hanging fruit" in terms of improvements to newcomers on their pitching staff.

The left-hander's average spin rate among tracked sliders was 2,749 rpm this spring -- well up from the 2,418 rpm he averaged on the pitch with Pittsburgh. His average four-seam spin also jumped from 2,401 rpm last season to 2,598 rpm in Spring Training.