ST. LOUIS – Mark McGwire, once one of the most revered sluggers in all of baseball, helped many St. Louis Cardinals teammates with hitting as he chased home run history. But it’s his work with one former All-Star pitcher that’s recently caught attention.

After he retired in 2001, McGwire acknowledged he used PEDs throughout his career, but he apologized and wanted to come clean with a second life in baseball.

McGwire joined the St. Louis Cardinals’ coaching staff from 2010-2012, developing relationships with players that eventually fostered a World Series Championship in 2011. The Cardinals averaged around five runs per game each season and improved in run production in each of their three years with McGwire coaching, so clearly something clicked.

Earlier this week, former Cardinals flamethrower Trevor Rosenthal revealed that McGwire and fellow hitting coach John Mabry were instrumental in helping him convert from an infielder to a reliable pitcher. Rosenthal says this was a surprise he didn’t realize until later in his career, but it happened largely because of the way he understood how to counter a hitter’s point of view as a pitcher.

In a Twitter thread Monday, Rosenthal says his first spring camp started off with hitting drills, which also included pitchers at a time when the designated hitter didn’t exist in the National League.

Rosenthal said McGwire and Mabry were among the first to welcome him to the batting cages though welcomed him with the question, “Are you lost?” Rosenthal said he came with a mindset to work, and both coaches “graciously met my persistence with their passion to teach the game.”

Rosenthal says the two would talk about hitter approaches and ways to identify weaknesses within swings. Years later, he took that to heart with swing-and-miss strikeout stuff and pitches that regularly clocked triple digits. Rosenthal said their feedback proved to be “a sharp edge to my competition” early in his career.

After bursting onto the MLB scene in 2012, Rosenthal pitched six seasons with the Cardinals, became trustworthy in a volatile closer role and earned an All-Star selection in 2015. Rosenthal broke the Cardinals’ single-season saves record with 48 that season, a big chunk of 121 he accrued in his St. Louis career. He also brought a different dynamic to the pitching staff with a strikeout rate of nearly 12 per nine innings.

Rosenthal, via Twitter, noted that McGwire consistently greeted him “with the biggest grin & firmest handshake” after every game he pitched in 2012. Mabry inherited the lead hitting coach role after McGwire’s departure in 2012 and carried on some similar philosophies that helped Rosenthal.

Though the Cardinals drafted Rosenthal as a pitcher in 2009, he played lots of infield in high school and college. Rosenthal says his work with McGwire and Mabry inspired him to dedicate his craft at pitching.

Currently an MLB free agent, Rosenthal explained his relationship with McGwire and Mabry as a hope for other athletes to discuss what has given them a professional edge while pursuing their passions.