When Campos called a pitch that appeared to be well off the plate a strike against Nick Markakis in the sixth, Showalter yelled something and was immediately ejected.
It was his first of the season and 20th of his career for Showalter. John Russell took over managing duties.
Showalter has been displeased with the strike zones in each of the games during the Angels series. Markakis complained in the fourth on Sunday when he was called out on strikes by Campos.