An Exciting Match At Base Ball To Come Off Soon. - The Empire Base Ball Club, of St. Louis, one of the strongest in the West, has challenged the Union club, also of this city, to a grand trial of strength for the championship of Missouri. The challenge has been accepted and the match will come off on the 26th inst., on the grounds of the Empire club, near the machine shop of the Pacific Railroad.
-Missouri Republican, June 13, 1867
E.H. Tobias, of course, has a great deal to say about this series:
The Union having challenged the Empire for a championship series of three games, the first was scheduled for June 26, on the Veto grounds, afterward known as the Compton Avenue Park, and located immediately adjoining the Pacific R.R. Machine Shops. Owing to a heavy fall of rain the game was called at the end of the fourth inning and, by mutual agreement, deferred until July 2, the score being 12 runs for the Empires and 10 for the Unions.
-The Sporting News, November 16, 1895
And that just makes sense, given how championships worked during this period. The Empires were the champions and if you wanted that championship, you had to challenge them to a series. They could accept the challenge or not. It was up to them. But it was the Union Club that needed to challenge the championship Empire Club and we have multiple sources that say that they did just.