NEW YORK — A week ago, it seemed like The Showdown. Today, it feels more like An Afterthought.

The Red Sox begin a three-game series with the Yankees tonight in Yankee Stadium, but the meeting has lost much of its urgency. When the Red Sox began this 10-game road trip, their once roomy advantage in the American League East race had been cut to a rather snug four-game lead.

But while the Sox steamrolled the Devil Rays and White Sox, winning six of seven, the Yankees stumbled in Anaheim and Detroit, losing five of seven games to put some distance between the two.

The Sox carry a comfortable eight-game edge into tonight, meaning the Yankees’ best chance lies with a sweep. Even that scenario would leave the Sox with a cushion and just more than four weeks remaining in the regular season.

A Red Sox sweep, however unlikely, would put an end to any hope the Yankees have of winning their 10th consecutive division title and cement the Sox’ first division championship since 1995.

Since executing a neat turnaround to their season at the end of May, the Yankees have, by virtue of their explosive offense, inched closer to the Sox, who have been in first place since the third week of April.

When the Yankees emerged from the All-Star break as if fueled by jet propulsion and feasted on some of the American League’s weakest links, comparisons to 1978 were not inevitable, but perhaps appropriate.

But invariably, the Yankees cooled and a more challenging patch of their schedule coincided with a more favorable stretch of sub-.500 opponents for the Red Sox. In winning 24 of 36 since July 20, the Red Sox have played at a .667 pace — less spectacular than the Yankees’ more torrid streak, to be sure, but impressive nonetheless.

And because the Red Sox held the lead to begin with, they had more of a margin with which to proceed. The onus fell to the Yankees to continue playing .800 ball, a pace no team could sustain. When the Yankees fell some, the Red Sox responded by pulling away enough to turn this week into the Yankees’ last, best hope.

“I don’t think the Red Sox have gotten enough credit for being (in first) as long as they have,” said one baseball executive. “People kept waiting for the Yankees to get hot and catch them. Well, they got very hot. But the Red Sox never gave up the lead. That’s impressive. It’s not easy to be in first place for five straight months.”

Some cited 1978 as the historical precedent, but that was never entirely appropriate. For one thing, this edition of the Yankees lacked a dominant starter like Ron Guidry, who won 25 of 28 decisions in ’78 and whose presence on the mound virtually guaranteed a victory that summer.

For another, the team’s aging rotation led to an overworked bullpen, necessitating a late-summer makeover by GM Brian Cashman. Gone are Mike Myers and Scott Proctor; here are Joba Chamberlain and Edwar Ramirez. Both have sparkled, but may have arrived too late to help facilitate a change in the standings.

Others saw the 2006 season as the blueprint, when the Yankees overwhelmed an injury-plagued Red Sox club with a five-game sweep at Fenway and pulled away like Secretariat at the Belmont in 1973. But unlike last season, the Red Sox have been the beneficiaries of extraordinarily good health this year. No starting position player — unless one counts backup catcher Doug Mirabelli — has spent time on the disabled list.

Even the seven-week absence of Curt Schilling didn’t crush the Sox; the team went 22-18 while he recovered from a weakened right shoulder.

Once this series is finished, the Red Sox will have only 10 games remaining on the road.

The Yankees, by contrast, will have 15, including three in Boston in the middle of next month.

By then, postseason positioning should be that much clearer. Unless the Yankees can replicate their play from late-July and the Red Sox correspondingly hurdle downhill at breakneck speed, the Yanks’ long division reign will be at an end and they — and not the Red Sox, as has been custom — will spend the final weeks extolling the virtues of the wild-card slot.

smcadam@projo.com