For now, though, they're enjoying a diamond honeymoon of sorts that thus far has taken them to the National League Championship Series.
The Cardinals and the Houston Astros are meeting in a rematch of last year's NLCS, but this is not old hat to these two. Eckstein, 30, who owns a World Series ring as a key member of the Angels in 2002, signed with the Cardinals in December. Grudzielanek, 35, who played in the 2003 NLCS for the Cubs, signed with the Cardinals in January.
Both came to the Cardinals known more for their offense. They delivered with the bats, posting twin .294 regular-season batting averages. But how much longer the Cardinals' season lasts could depend on how well their gloves work. Runs are expected to be at a premium.
During the regular season, St. Louis led the Major Leagues with 196 double plays, with the middle infielders at the heart of most of those.
"Double plays are key to winning championships," Eckstein said. "No matter the situation, we try to turn everything."
How did two guys who wore different uniforms come to a different team and mesh so well? Last year's shortstop Edgar Renteria headed to Boston and second baseman Tony Womack wound up with the New York Yankees.
It began with a simple decision on the part of manager Tony La Russa. He placed the players' lockers beside one another at Roger Dean Stadium in Jupiter, Fla., at the start of Spring Training.
After Tuesday's workout, hanging side-by-side in front of adjoining lockers in the Busch Stadium clubhouse were Grudzielanek's No. 12 and Eckstein's No. 22 home whites.
"We talked a lot and we had to get comfortable," Grudzielanek said. "We were in the same groups all the time. I think Tony did it for a reason. He needed to, because we needed to get acquainted with one another, learn each other.
"It was nice to do that in Spring Training," Grudzielanek said. "I can't stress how important it was to actually get Spring Training under our belts, those four or five weeks there to work together."
Magic happened quickly.
Double-play combinations are sometimes tricky because players have specific ideas on when to receive the ball at the bag and the type of throw that comes. But both had been around long enough to adjust to one another. Grudzielanek said it was so smooth that Eckstein's low arm angle -- he's 5-foot-7 -- didn't even take an adjustment for him. The fact that, according to Grudzielanek, Eckstein continues to work on his arm strength and throw with as much zip as a bigger shortstop helps.
Grudzielanek, who led NL second basemen with a .990 fielding percentage (seven errors), has Eckstein's respect as a defender.
"He's a Gold Glover," Eckstein said.
If that turns out to be true, both of them might be placing gold on their fingers soon.