"The front office is always looking at how the team can get more versatile and ways to match up guys with other guys depending on their strengths," said manager Bob Melvin. "Certainly Alberto can hit from both sides of the plate, and it seemed like a natural fit."
The experiment endured a rocky beginning, as the first batted ball of the game went through Callaspo's legs. When Seattle leadoff hitter Abraham Almonte rounded first, second baseman Nick Punto threw behind him. The throw was wide of Callaspo for an error on Punto.
Callaspo would stay on the field for six more innings without any further defensive issues, before being replaced by Daric Barton as a pinch-runner in the seventh.
The 5-foot-9 Callaspo, who has spent time at every other infield position besides catcher, as well as in the outfield corners, began work at first base in the early going of Spring Training. He borrowed Barton's glove for much of the time, but has since broken in his own that was also expected to debut Thursday.
"It's a work in progress for anybody who's learning a new position," said Melvin. "It is the infield. He can catch a grounder.
"It's going to take him some time to get real comfortable out there at first base, but each time he was out there in spring he looked better and better."
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.