Commissioner of Baseball Bud Selig, far left, shakes hands with MLB Players Association director of player relations Tony Clark, as MLBPA Executive Director Michael Weiner, second from left, and Boston Red Sox's Andrew Miller, second from right, leave after the news conference announcing the new CBA. (Bebeto Matthews/ASSOCIATED PRESS)

Baseball’s new collective bargaining agreement is so monumentally symbolic for the sport, and such a shock to our cynical systems, that millions of fans, accustomed to 35 years of labor warfare or steroid disgrace, may suffer from the same delighted whiplash. We hardly know how to cope with optimism in such unaccustomed quantities.

If we step far back for a sweeping view, this is a remarkable moment. Less than four years after the shame of the Mitchell Report, the sport has done almost everything right this time, and accomplished it in a sane, private, adult manner, at a time when every other sport threatens to lose its mind.

Whatever baseball hasn’t nailed correctly in Tuesday’s CBA, it can probably tweak in the future as long as the current chastened climate — funny how decades of mortification begets temporary modesty — remains in place.

For a generation, it has been a second calling for true baseball fans, as well as critics, to take turns berating owners, commissioners, union heads, agents and players. Duty called. To be a fan was to love the sport while battering those who made millions while ignoring their responsibilities as stewards.

However, enough time and pain teaches anybody lessons. Eventually, baseball learned.

The CBA stunner was in drug testing. Who thought baseball would take blood to test for human growth hormone before the NFL with all its suspicious behemoths? But now baseball has opened that door.

As the first North American pro sport to start HGH testing, baseball will take an incremental approach, beginning next spring training. An in-season program won’t begin until 2013, earliest. We’ll need to see how effective that testing is. But such a fundamental change in stance by the union, a switch that seems impossible to reverse, deserves lots of praise.

Baseball now has five more years of labor peace, bringing its streak to 21 seasons. But something far more fundamental is in play: Neither side questions the basic viability of the current economic structure. “The system” itself isn’t under attack, as was the case with the NFL lockout, the catastrophe in the NBA and looming issues for the NHL.

Baseball, partly by luck, has evolved an economic structure that allows complex detailed negotiation by pros, not ultimatums by big egos.

Suddenly, the sport is solving problems a half-dozen at a time. In recent days, a new owner was found for the distressed Astros. Someday, the Dodgers, ravaged by the moronic McCourts, will be auctioned. And, now, the CBA arrives just in time so we can all say, “Thanks.”

●With Houston’s move to the American League in 2013, the leagues will be balanced; so, schedules will become more sensible (no 18 Nats-Marlins games per year).

●A new “hard-slot” system in the amateur draft may pinch the contracts of future Stephen Strasburgs and Bryce Harpers. Is it “fair?” No, but what good is a sanctioned monopoly if you never use it?

●Other new rules will impose penalties so severe for going “over slot” for an entire draft class that it’s unlikely any team will again land a haul like the Nats did in August when they grabbed Anthony Rendon, Alex Meyer, Brian Goodwin and Matt Purke.

The Nats saw the new rules coming, and no doubt helped precipitate their arrival by picking three players who might’ve blossomed into truly elite picks in ’12. The Nats gambled while the system still allowed it, though it annoyed other teams and MLB brass.

●The Nats are also a team deeply impacted by the addition of a second wild card in each league; starting next season, the two wild cards will have a one-game playoff to reach the normal eight-team postseason. So, the playoffs will always start with a sudden-death doubleheader.

Good idea? Everybody’s antsy; nobody knows. I suspect it’ll be great.

Why? It addresses two problems at once. First, wild-card teams, such as this year’s Cardinals, have far too good a chance to win the World Series. Home-field advantage helps in baseball, but not much. So, a wild card starts October on almost equal footing with an over-100-win division winner. That’s not fair.

Starting now, every wild card has a 50-50 chance to get knocked out on Day One. So, powerhouse teams such as the Red Sox or Yanks are going to have added incentive to win their division, not settle for a wild card. A great pennant race, even a classic battle between 100-win teams, matters again.

The second wild card also will affect another class of teams — those very much like the rising 80-81 Washington Nationals.

Crunch the numbers since the eight-team postseason began, and the impact is clear. Now, if you win 90 games, you’re a lock to make the playoffs. That’s the magic number. (Starting in ’96, 44 of 45 with 90-or-more wins would’ve made it under the new system.)

Of the 13 teams that won exactly 89 games since ’96, just four made the playoffs. In the new system, 11 of the 13 would’ve made it. Big difference.

So, if you’re the Nats, here’s your new reality: 89-90 wins virtually locks you into October, 86-88 might, while 84-85 gives you a prayer.

Commissioner Bud Selig, 77, was as responsible as anybody for the bad old days. Yet he has done what few people in any industry can ever accomplish. He has survived, adapted and, finally, undone most of his sport’s and his own biggest blunders. He has helped build a functioning owner-player consensus by serving as an institutional memory that vividly recalls the full price of bitter failed labor negotiations.

In the end, he has left an excellent legacy that, frankly, I never would have imagined possible just a few years ago when his name was still connected to the worst of baseball buzzwords from “collusion” in the ’80s to “The Strike” in the ’90s to the steroid era scandals of the ’00s.

This is his day. Selig, who always claims an historian’s sensibility and who, indisputably, adores the game up to the legal limit, has outlasted and outwrestled a tormented baseball period that started almost half his life ago.

Those who don’t learn from history are, as everyone knows, condemned to repeat it. Bud Selig learned. He didn’t repeat, but rather, rewrote his own, and his game’s history.