"After seven innings against the Seattle Mariners on Saturday, Jason Giambi had to tell A's manager Bob Geren his tank was running on empty.

Giambi, 38, already had legged out an infield single and sprinted after a foul ball that landed just out of his sliding reach.

"I told Bobby, '(The legs) are dead'," Giambi said.

In the A's home-opener on Friday night, Giambi ran all the way to third after he hit a slow ground ball to pitcher Ryan Rowland-Smith, whose errant throw went past first base and down the right field line.

"This is way too much running for me," Giambi said. "This is a little out of control for me. This is way too much running this early in the year."

Giambi's infield single led off the fifth inning. He hit a sharp ground ball up the middle that Mariners' second baseman Ronny Cedeno gloved behind the bag. But Cedeno could not get the ball to first in time to beat the hustling Giambi.

The hit was followed by a pair of flyouts from Matt Holliday and Nomar Garciaparra, then Giambi got to jog home when Jack Cust homered.

"If Jack hadn't hit the ball out of the ballpark, it'd have been like an auto parts store out there," Giambi said tongue-in-cheek. "My hamstrings would have fallen out. My groins would have fell out. I would have been done for the year. Thank God that ball got out."

Geren didn't hesitate to remove Giambi. Garciaparra moved from third base to first, and Bobby Crosby took over at third. Giambi is expected to start today's game.

"He's been playing hard," Geren said of Giambi. "That's all you can ask. You go hard, and when you can't go, you can't go. I love the effort.""