New York Yankees first baseman Mark Teixeira (laying on the...

New York Yankees first baseman Mark Teixeira (laying on the ground) is helped up by head athletic trainer Gene Monahan (center) after being hit by a pitch in the bottom of the first inning against the Boston Red Sox at Yankee Stadium. (June 6, 2011) Credit: Christopher Pasatieri

Fox has a heck of a matchup for its regional baseball coverage tomorrow, one that features the World Series champions of 2008 and '10, representing two of the six biggest markets in America.

Yup, Phillies vs. Giants is a television executive's dream.

But wait: That game will be on in only 18 percent of the nation, not including seemingly natural areas of interest from Baltimore and Washington to Los Angeles and San Diego.

What gives? This: Fox's other game showcases the champs of '07 and '09, the Red Sox and Yankees, which remains the most durable, reliable draw in the sport -- by far.

That might not seem like news more than a decade into the most recent era of the rivalry, a period in which Fox and ESPN all but automatically have grabbed those games on weekends.

But it is worth pausing to appreciate it, a long-running reality show that regularly delivers and whose novelty seems not to have worn off even in a time of long games and short attention spans.

"From our point of view, this rivalry has lost none of its edge," said Mike Ryan, VP of programming and acquisitions for ESPN, which will show Sunday night's game.

"Year in and year out, game in and game out, the numbers tell us people are interested in the Red Sox and the Yankees."

Mike Mulvihill, Fox's senior VP for programming and research, said that to be fair the rivalry is "probably not as hot as it was in 2003 and 2004."

But . . . "It's still by far the best thing we have going in regular-season baseball.''

Over the past decade ESPN has averaged 3.96 million viewers for Yankees-Red Sox games on Sunday nights. All other games have averaged 2.18 million.

Those figures mostly have held up in recent seasons, including 3.93 million viewers for the two matchups so far this year.

On Fox, weeks in which Yankees-Red Sox games have been part of regional coverage have averaged 2.6 percent of homes -- 44 percent better than other weeks.

The key to such ratings power is not just that New York and Boston are big, baseball-oriented markets. It is that the Yankees and Red Sox are draws elsewhere, too.

Hence Fox's decision to show that game in West Coast cities from Seattle to San Diego rather than San Francisco's Giants.

Mulvihill said it is a bit of a shame that less than 20 percent of the nation will get Phillies-Giants, but such is "the power that the [Yankees-Red Sox] rivalry has outside the home markets."

Would it be good for baseball and its TV partners to have more nationally attractive rivalries develop? Sure, Mulvihill said. But it also is nice to have at least one given.

"I would not wish for either the Yankees or Red Sox to go into a decline," he said. "It would be great for us if they were good for another 15 years."