Under Brenly, the D-backs went on to win the World Series in 2001 and Showalter went on to manage in Texas and Baltimore, where he's now finishing his third full season.
Asked if he's a different manager now then he was back then, Showalter didn't quibble.
"God I hope so," he said, seated in the first-base-side visitors' dugout for the first time. "Are you any different now than when you were 12? We all learn from experiences and things that we go through. If I knew I was going to hurt that little girl's feelings, I wouldn't have pulled her pigtails in the third grade. You learn things.
"People say, "I'd never change a thing.' You never know how things are going to turn out. I was very proud of what I was allowed to be a part of [in Arizona]. It was special."
D-backs fans certainly haven't forgotten. They gave Showalter a warm ovation when he was introduced by the public address announcer after the Orioles scored a run in the top of the first inning. Leaning on the dugout railing, Showalter tipped his Orioles cap to the crowd.
The D-backs officially expanded into the National League in 1998 and Showalter managed their first 486 regular-season games, finishing 250-236, a .514 winning percentage. In their second season, the D-backs won 100 games and lost to the Mets in the first round of the 1999 playoffs.
Showalter praised the development of a facility called Bank One Ballpark in his day and the organization that hired him to build a team from scratch upon losing the managerial job after four seasons with the Yankees.
Showalter has been back for alumni ceremonies since then, but never to manage a game.
"It was a great experience," he said about those days. "It made you appreciate an organization and baseball. I was fortunate to have ownership that did some things to put us in position to be competitive quickly. They picked great people who came in and took it to the next level. They've made some really good decisions here along the way."
Barry M. Bloom is national reporter for MLB.com and writes an MLBlog, Boomskie on Baseball. Follow@boomskie on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.