Fenway Park West.

It's in Oaktown:

Some of the A's younger players had to be shocked at the sight of it, let alone the sound. It was the bottom of the ninth inning Monday night. A promising threat had suddenly died on Bobby Crosby's double-play grounder, forcing extra innings. And the place went absolutely nuts. Sheer bedlam among the 20,000-odd fans still in attendance.

Pro-Boston crowds have been a staple in Oakland since the A's moved west in 1968, just a year after Jim Lonborg and Carl Yastrzemski carried the Red Sox into the World Series, but this was radical. This might as well have been Fenway. There can't be another fan base in the country, at any level, where the sentiment shifts so thoroughly for an opposing team based some 3,000 miles away.

Bruce Jenkins in the SF Chronicle.