ONE of the great things about baseball, Buck Showalter said, is that every day the game will surprise you.

He said this with the air of a man who enjoys surprises, and if that is the case, Buck Showalter must have been mighty surprised – and mighty pleased to see what happened to his team and his ace Friday night at Shea Stadium.

Then again, maybe Showalter was not so surprised.

The Mets beating up on the Arizona Diamondbacks and Randy Johnson has become business as usual, around here and back at the BOB.

Including last year’s Division Series, the Mets have beaten the Diamondbacks in 9 out of their last 11 games heading into last night’s game at Shea.

If ever a team seemed to have another team’s number, the Mets seem to have Arizona’s.

Friday night, they beat Johnson like the drums these 21 kids were pounding on last night in what passed for pre-game entertainment.

And for what it is worth, this weekend’s series, which was expected to be a showdown between the two leading candidates for the NL wild card, has turned into something of a joke.

Before last night, the Mets had put 5½ games between themselves and the D’backs, and a sweep of the series would have left Showalter and his boys with some series ground to make up, with precious little time to do it.

That is why the real surprise was that Showalter was as relaxed as he appeared to be before last night’s game.

Then again, that is the difference between toiling out of a bunker in the Bronx for The Boss, and managing for Jerry Colangelo in the Valley of the Sun.

“Beats the hell out of working,” Showalter said with a grin. “Pressure? I think in all phases of life, there’s pressure, but believe me, things have been a lot tougher than this. Personal things, family problems, your children, those things are a lot tougher to deal with than baseball games. You’ve got to keep a grip on reality.”

Those were luxuries not afforded to Showalter during his four seasons as Yankee manager, when it was win or walk.

In Phoenix, Showalter actually drew paychecks for 28 months for not managing, time that he spent designing baseball in the Valley from the grass on up.

Showalter, who enjoys control, designed the team logo, the uniforms, the Diamondbacks clubhouse, and of course, the manager’s office, with its centerpiece reproduction of Rodin’s sculpture of The Thinker.

Contrary to popular belief, Showalter did not pose for it, nor is he the one who figured out it would be best to go with nine innings, three outs and three strikes.

Everything else, is his. The Diamondbacks are a team truly created in their manager’s image, and this year, the image has a slight coating of tarnish on it.

Showalter won the West Division with the Diamondbacks last year, in only their second season, but then, they were an expansion team in name only.

Showalter had Colangelo’s fat bankroll with which to buy players, and a healthy crop of free agents on which to spend it.

Still, success that comes that quickly and easily creates the expectation of more and greater success, and fast.

As of last night, the Diamondbacks were in second place in the NL West, 3½ games behind the San Francisco Giants. But they had a better chance of catching them than the Mets, who had five fewer losses.

“We’re proud of the expectations we’ve created,” Showalter said. “But obviously, with the expectations comes the danger of not meeting them.”

The case could be made that last year, the Diamondbacks did not live up to expectations, either.

Winning a division in your second season is great. However, once a team has won it and enters the elite company of the other three teams with a chance to reach the World Series, it ceases to be an expansion franchise.

Now, it is expected to play ball with the big boys. And in their first playoff test, the Arizona Diamondbacks got smoked by a Mets team that needed to go to overtime – an after-the-season one game playoff with the Cincinnati Reds – just to sneak into October.

Outscored in the four-game series, 27-15, and held to a .206 team batting average by Mets pitchers, probably the biggest shock of all to the Diamondbacks system was the way the Mets manhandled Johnson, the 1999 Cy Young Award winner.

They routed him, 8-4, in Game 1, and neither he nor his team seems to have recovered.

“They’re different teams, and it’s a different year,” said Bobby Valentine, seeking to downplay what has become obvious to everyone else. “You’d like to think so, but there’s no carryover whatsoever.”

That, of course, should have been Showalter’s line.

But then, he knows as well as anyone that the numbers don’t lie. For all their strengths and their early successes, there is one thing the Arizona Diamondbacks can’t seem to do.

Beat the New York Mets.

That is why the Little General is hoping the game that he loves so much will surprise him once again, because if things stay as they are, he and the Diamondbacks can look forward to early-fall golf in Phoenix again this year.

“That’s the beautiful thing about this game,” he said. “Just when you think it’s got its foot on your throat and it’s not going to let you up, things change. Sometimes when you think things can’t get any worse, all of a sudden, they get better. We got a lot of guys on this club with just one thing left to put on their resumes, a World Championship.”

And the one line they would like to erase from their resumes? Their record of futility against the Mets.

Starting with last night, they had precisely two games left to do it.

Now, that would be a real surprise.