Bill Kelsoe, in A Newspaper Man's Motion-Picture Of The City, makes two references to the Atlantics of Brooklyn playing in St. Louis. He mentions a game played between the Reds and the Atlantics on July 29, 1874 and another between the Empire Club and the Atlantics on May 2, 1875. When I read those references, I was immediately skeptical (as seen in this post).
The Atlantics did come to St. Louis in 1868. They defeated the Union 68-9 on June 27th and then beat the Empire 53-15 two days later. This is the only record of an Atlantics' visit to St. Louis that I can find. The only other link that I can find between St. Louis and the Atlantics of Brooklyn is the fact that Lip Pike, Dickey Pearce, and Jack Chapman all played for the Atlantics before joining the Brown Stockings in 1875.
My assumption was that Kelsoe, who in writing his book used both the records of numerous St. Louis newspapers as well as his own personal recollections and those of his acquaintances, had simply confused the 1868 visit of the Atlantics of Brooklyn with games played in 1874 and 1875 by a St. Louis amateur team also called the Atlantics. He was, after all, writing almost fifty years after the fact and these things happen. When going through my notes, I found a reference to an Atlantic Base Ball Club in St. Louis that supports my assumption. This Atlantic Club was an amateur team that played its home games at the Compton Avenue Base Ball Park owned by Thomas McNeary.
In the April 5, 1875 edition of the St. Louis Globe, there is an account of a game played between the Reds and the Atlantics in which the Reds emerged with a 32-4 victory. Playing for the Atlantics that day were Libby, Price, Williams, Jones, Rippy, Myers, Kelly, Mueller, and Devinney. The Globe states that it was the intention of the Atlantics to join the Missouri State Association that year and compete for the amateur baseball championship of Missouri. The officers of the Atlantics were listed as J. Walter (president), E. Hogan (secretary), George Waugh (treasurer), and L. Meyer (director).
One has to assume, based on this evidence, that the team that defeated the Reds at the Compton Avenue Park in 1874 and the team that was beaten by the Empire at the Grand Avenue Park in 1875 was the Atlantic Base Ball Club of St. Louis and not the Atlantics of Brooklyn.