The first game to be played at American Park was on April 9, 1884. It was an exhibition game against the then National League Cleveland Blues. The Reds first official home opening day at American Park was on May 1, 1884 against their American Association rival the Columbus Buckeyes. Cincinnati lost that game 10-9 in heartbreaking fashion.
The season itself saw a good deal of competition between the Reds and the Unions. Although many called the Union the "Onion League" due to its lopsided distribution of talent, the Cincinnati Unions were a fairly strong team and drew fans away from the Reds. Once the Union folded, the Reds opted to remain at Findlay and Western, and would continue to do so for the better part of nine decades. Thus the Reds had the city to themselves in 1885.
Although the Reds were not participants in the 1885 World Series, their ballpark was. The contest, between the Chicago White Stockings of the NL and the St. Louis Browns of the AA, staged some of its games at neutral sites. The Reds' ballpark was the site for the final two games of the Series, a disputed match that officially ended in a draw.
When the Reds returned to the National League in 1890, the name of the park would come to be known as League Park, in reference to the team's original and now current circuit. In those days, the National League was typically referred to in media as "the League", since there was only one "League" and (for ten years) one "Association".