But this visit has little to do with nostalgia and all to do with assisting the Dodgers in getting to a World Series, just as he did in red and white two years earlier. It's an intriguing dynamic -- a hitting coach who spent three years helping build the Cardinals' offense into an elite unit will now try to point the Dodgers' pitching staff toward those hitters' holes.
"In our meetings today, Mac probably had a lot more input than he would on another club," Dodgers manager Don Mattingly said Thursday before the National League Championship Series begins Friday at 7:30 p.m. CT live on TBS and Postseason.TV. "He obviously does know their hitters fairly well and what they try to do and where he thinks [we can get] some of them out and where their weaknesses would be."
But better than anyone, McGwire knows the depth of that challenge. Having served as the Cardinals' hitting coach from 2010-12, his impact is evident all throughout an offense that boasted some of the best numbers in the league this season.
"He had lots of young hitters that he helped develop into what we're seeing right now," Cardinals manager Mike Matheny said. "You can go through that clubhouse and realize that he's got his fingerprint on quite a few of them, and their approach and their professionalism. … He has a great sense of how to teach the art of hitting and how to individualize it as good as anybody I've seen."
McGwire preached the mental more than the mechanical, instilling an approach that some of his hitters described as patient aggressiveness. The Cardinals walked more often and cut down on their strikeouts. His philosophy was passed down to John Mabry, who assumed the position when McGwire left during the offseason for Los Angeles so that he could be closer to his family.
From afar, McGwire watched the Cardinals lead the league with 783 runs scored and post the highest batting average with runners in scoring position (.330) in at least 40 years.
"Mark was a big influence on myself and the rest of the younger hitters when we first came up," Daniel Descalso said. "The guy has a wealth of knowledge that he passed along to us. And he was always very positive. No matter what kind of struggle you were going through, he was there to work and talk hitting. He was a great guy to have around the ballclub."
Descalso is one of eight hitters on the Cardinals' postseason roster who never knew another Major League hitting coach until this season. He was a part of a young core of drafted-and-developed talent that McGwire helped shape in their formative years.
"He allowed me to escalate my game at this level at the right time," David Freese said. "He definitely had a huge impact on a lot of us guys with not a lot of experience, especially in 2011 on that run [to the World Series]."
It was McGwire who, early last season, predicted a breakout year for Allen Craig. McGwire joked, at the time, that the Cardinals would do well to sign Craig to a multiyear deal as soon as possible. The Cardinals ended up locking him down this spring.
McGwire was gushing about the Cardinals' injured first baseman again on Thursday.
"He's probably one of the most pure RBI guys that I've ever worked with that is just really coming into his own," he said.
At the end of the 2012 season, McGwire was vocal in encouraging the Cardinals to give Matt Carpenter a try at second base so that Carpenter would be able to dent the starting lineup. The Cardinals passed that challenge to Carpenter, who took over at the position this year and produced numbers worthy of MVP consideration.
"It wasn't hard to see the talent that he had," McGwire offered. "It was just a matter of him getting an opportunity."
McGwire remains invested in these former pupils, too. He left behind not just professional relationships, but personal friendships that have outlasted his coaching tenure in St. Louis. Several Cardinals players said they have remained in contact with McGwire throughout this season. Most of their back-and-forth has little to do with baseball.
Many were also appreciative of the time McGwire took to reach out to them this offseason before news of his departure became public. He wanted each to understand that it was nothing more than family obligations that pulled him away.
"He truly cared for everybody that he worked with and wanted to see us be successful," Carpenter said. "Even this season, he cares for these guys. Obviously, we're going to be playing against each other and he's going to be playing for those guys, but he means a lot to a lot of guys in here."
"It was a tough decision to switch, to make a change," McGwire added, shortly before the Dodgers held a late afternoon workout on Thursday. "I did it for my family. It has worked out really, really well. And here we are together, playing against my former teammates. It's going to be fun."