Some baseball historians have suggested that Dunlap's accomplishments during the 1884 season should be discounted due to the lesser talent pool in the Union Association. In 1885, the Union Association was disbanded after only one year, and the St. Louis Maroons joined the National League. Although his batting average dropped 142 points to .270 in 1885, Dunlap continued to be one of the best defensive second basemen in the major leagues. He led the National League's second basemen in 1885 with a .934 fielding percentage and ranked second in assists (374), putouts (314), and range factor (6.49). Dunlap spent a third season with the Maroons in 1886, and hit for the cycle on May 24. However, the Maroons were in financial distress, and rumors spread that the team might disband.