The game of Base Ball played at Gamble Lawn yesterday, between the Union and Empire Base Ball Clubs, resulted in the complete victory of the former. The score was as follows: [Union 53, Empire 15.]-Missouri Republican, May 15, 1862
The game was played for the Championship.
Just for a bit of context, while this game was being played Stonewall Jackson was routing Union forces in the Shenandoah Valley and McClellan had already landed his forces in Virginia and was (slowly) marching on Richmond. The Civil War was in full swing.
What interests me here is the reference that the game was "played for the Championship." Most likely this was one of a series of games between the Empires and Unions for the championship rather than a winner-take-all championship game. There appears to have been a championship series between the clubs in 1861 and I doubt that they would have changed the format so radically in 1862.
I should also mention that this is one of the few match games I'm aware of that was played between two senior clubs in St. Louis during 1862. There was plenty of baseball going on during the war but match games between senior clubs still appears to have been a rare occurrence.