An opener, for the Rays, refers to a pitcher who starts the game but will generally face only three to nine batters, depending on matchups. Often, the pitcher who follows the opener will throw five or more innings, putting him in a de facto — though delayed — starter’s role. No team has ever done this.
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Yet no matter their roster makeup, the Rays actively try to devise different ways to win. Blow up the traditional idea of starting pitching? Sure, why not? It seems to be working. Before May 19, their first game using an opener, the Rays had a 4.43 earned run average, ranking 22nd in the majors. Since then, through Monday, their E.R.A. ranked fourth, at 3.47.
Source: Tyler Kepner, The New York Times