BOSTON — The good news at Fenway yesterday? Start with the 15-hit explosion and the four homers, a power display that helped seal the Red Sox weekend sweep.

The bad news? Beyond Josh Beckett’s gopher-ball issues, there was this: now that the Milwaukee Brewers have left town, the Sox don’t face another National League team until June 13.

Interleague games have become layups for the Sox. Since the 2006 season, the Sox are an astounding 31-8 against N.L. opponents, a winning percentage of nearly .800.

When they’re home, the record is 18-3, having won six in a row and eight of the last nine.

What is this — the NBA?

In that span, the Sox have beaten good National League teams, bad ones and teams — such as the Brewers — in between. They’ve beaten teams from each of the three N.L. divisions — East, Central and West. They win at Fenway, and on the road (13-5), too.

Were it not for the appearance of N.L. teams on the schedule —against whom they were 16-2 — it’s very likely that the injury-plagued 2006 Red Sox would have finished under 500. Even when the Sox have been bad, they’ve still been good against teams from the National League.

Toss in the Sox’ four-game sweep of the Colorado Rockies in last October’s World Series, and the number moves to an unfathomable 35-8 and 20-3 at home.

Theories might abound, but answers were in short supply in the Red Sox clubhouse yesterday following their 11-7 win.

“No idea,” said Tim Wakefield. “Wish I could help you, but I have no idea.”

How about you, Alex Cora? Any clue?

“None at all,” said Cora, “other than to say we adjust to any situation. I guess it’s just baseball.”

“Just one of those things,” offered a semi-helpful Jason Varitek.

Without much direction, here are a few possibilities.

•The American League is the clearly superior league, and the Red Sox are one of the better teams in the better league. Therefore, some of these matchups are really mismatches.

•Intimidation. The Sox are almost literally unbeatable at home against the N.L., perhaps because young teams — such as the Brewers – are unaccustomed to the Fenway environment.

If Fenway provides an obvious home-field advantage against good American League teams such as the Angels, that’s exacerbated when the opponents are inferior and inexperienced teams from the other league, stepping into the Fenway cauldron for the first time.

“You get some of that at Wrigley (Field),” said hitting coach Dave Magadan, who spent the vast majority of his 16-year playing career in the National League. “But it’s a little more in-your-face here.”

•Advance scouting. The Sox spend more resources on advance scouting — in terms of manpower and detail — than almost any other team in either league. In a series against unfamiliar opponents, the smallest detail and slightest edge in preparation can make the difference.

Perhaps this is merely cyclical. After all, it wasn’t that long ago that the Sox dreaded crossover games. When interleague play was introduced, in 1997, the Sox were a poor fit.

As recently as 2002, the Sox were an abysmal 5-13 against N.L. teams. When they reached the ALCS in 1999, they were a putrid 6-12 against the N.L. Even when they won their first of two championships in 2004, the Sox were just 9-9 when matched with N.L. teams.

Back then, they weren’t athletic enough to keep up with N.L. teams and their pitching staff wasn’t nearly as deep. In the late 1990s, the starting rotation had Pedro Martinez and an undistinguished supporting cast.

“I seemed to remember a lot of games where our starters were going about four innings,” recounted Varitek, second in seniority on the team.

In contrast to this edition of the Red Sox, those teams often relied too much on production from the DH, making them especially vulnerable on the road when use of the DH is prohibited.

Of course, the Sox’ current DH, David Ortiz, has been the club’s best run producer in the recent run of success, but the Sox are more evenly balanced with their lineup and generally find a way to get Ortiz into two of every three away games in N.L. parks.

“Even when we don’t,” Cora pointed out, “we’ve got (Kevin Youkilis) at first and David on the bench to pinch-hit. That’s a pretty good bench.”

And whatever the formula may be, a pretty good track record.

Only 26 days until the schedule-maker serves up the next victim.

smcadam@projo.com