Descalso, who played second base at Triple-A Memphis this year, got the call at third against Pirates right-hander Charlie Morton on Wednesday. The lefty-swinging infielder was chosen over Aaron Miles. Descalso was drafted as a third baseman out of Cal-Davis in 2007, but has played second for the bulk of his professional career.
"I'm just happy to be here," Descalso said. "I've been working over at third base for the last few days and previous weeks before that, so I'm feeling pretty comfortable over there. I'm trying to draw on my past experience over there, go out there and do what I do. I was taking some ground balls over there, just in case. It's not like I'm totally new over there."
Descalso officially made his Major League debut on Saturday, when he was introduced as a pinch-hitter, then replaced for another pinch-hitter before he got to bat.
Starting at an unfamiliar position is not the ideal way to get his first live game action, but manager Tony La Russa is confident in Descalso's chances at third.
"We've worked him out there," La Russa said. "He catches the ball. He's got plenty of arm to play it. We think he's a better fit than Miles there. It gives him a chance to play. He has played third before. You don't want to put a utility-man label on somebody yet. But if he can play different positions and it helps him get in a Major League lineup, it's good."