SCOTTSDALE, Ariz. -- In hot pursuit already of more swing-and-miss stuff from starting pitchers and relievers, the Cardinals made a move to acquire 6-foot-4, 180-pound right-hander Riley O'Brien from the Mariners.

O’Brien, 28, was a Pacific Coast League All-Star in 2023, striking out 86 over 55 innings with Triple-A Tacoma. He was 2-5 with a 2.29 ERA, making three starts and notching nine holds and 15 saves in 19 opportunities.

The deal was finalized late Sunday night and announced via MLB’s transactions page. A Cardinals source said the club is still awaiting final approvals and player notification, but the deal is close to being finalized. The pending Minor League free agent will likely be added to the 40-player roster to avoid being plucked out of the Rule 5 Draft. He was assigned to the Memphis Redbirds' roster on Monday.

Following a 71-91 finish and the club’s first last-place division finish in 33 years, the Cardinals are planning to be active in the free-agent and trade markets for pitching. Some of that activity could come this week with MLB’s GM Meetings, which will get underway in Arizona on Tuesday.

Thin on pitching and further shorthanded when veteran right-hander Adam Wainwright opened the 2023 season on the injured list, the Cardinals' pitching staff struggled throughout the season. They finished with baseball’s 24th-ranked overall ERA (4.79), 26th-ranked starters' ERA (5.07) and 23rd-ranked relievers' ERA (4.47).

Sellers at the MLB Trade Deadline for the first time in decades, the Cardinals dealt starters Jordan Montgomery and Jack Flaherty and relievers Jordan Hicks, Chris Stratton and Génesis Cabrera for lefty reliever John King and a host of prospects.

Now, the franchise hopes to use this offseason to restock its pitching -- both in the starting staff and the bullpen -- throughout one of the most critical offseasons in decades. Miles Mikolas and Steven Matz are the only two solidified starters under contract for 2024. Zack Thompson and Dakota Hudson are possibilities for the rotation if the Cards are unable to lure multiple elite arms to St. Louis via free agency or trades.

O’Brien graduated from Shoreline High School in Washington, the same school that produced left-handed star Blake Snell, who is the likely winner of the NL Cy Young Award following a dominant season with the Padres and is one of the most high-profile pitchers available in free agency this offseason.

O’Brien’s grandfather, Johnny, played six years in the Majors, including part of the 1958 season with the Cardinals. O’Brien was an eighth-round pick of the Rays in 2017, and he’s pitched two MLB games since then -- one with the Reds in 2021 and one with the Mariners in '22. He was traded from the Rays to the Reds on Aug. 28, 2020, and he was designated for assignment on April 13, 2022. In six Minor League seasons, he has 504 strikeouts in 439 1/3 innings pitched. He’s thrown 60% of his pitches for strikes, and he has a 10.32 strikeouts-per-nine innings ratio.