UPDATED: 7:06 p.m.

While it was convenient to view the San Francisco Giants, Philadelphia Phillies and Atlanta Braves, the three best teams in the National League, as being similarly constructed — deep in pitching, thin on offense — the fact of the matter is the Giants’ level of desperation for a big bat went well beyond that of the other two. Entering Wednesday, the defending World Series champs ranked 15th in the NL in runs, 13th in batting average and 15th in OPS.

And so, if one of the three contenders was going to part with the blue-chip pitching prospect the New York Mets were seeking in exchange for veteran outfielder Carlos Beltran, the prized target of this trade season, no one should be surprised that San Francisco was the one. The Mets and Giants agreed to the trade Wednesday, and await the outfielder’s permission to complete the deal.

The Giants’ willingness to say yes to the Mets’ demand for top pitching prospect Zack Wheeler — while the Phillies and Braves held firm to their refusals to give up Jarred Cosart and Mike Minor, respectively — made the deal happen.

On a dizzyingly busy day in baseball — when the St. Louis Cardinals traded 24-year-old center fielder Colby Rasmus to Toronto, Los Angeles Angels pitcher Ervin Santana threw a no-hitter, and the Pittsburgh Pirates filed a formal complaint over an umpire’s apparently blown call in the 19th inning of a crushing loss in Atlanta the night before — the Giants’ trade for Beltran was the biggest story line, seeing as how it could alter the balance power in the NL.

The Giants, with a three-game lead over Arizona in the NL West and the lowest ERA (3.12) in the league entering Wednesday, likely would win the division even without making a big deal for a bat. But with a fanbase that is poised to fill AT&T Park to 100 percent capacity for the entire season, and with a young core of pitchers that gives the franchise a defined window for winning championships, the Giants are aiming higher than merely a playoff berth.

Beltran, posting a resurgent .289/.391/.513 season at age 34, gives the Giants the middle-of-the-order bat they desperately lack. The Giants were in a similar position a year ago, but found salvation in the form of catching phenom Buster Posey, a midseason call-up. But this year, Posey, their primary cleanup hitter for the seasons first two months, was lost for the season in May after a violent collision at the plate. Without him, the Giants’ offense went from inconsistent to anemic. In one recent game, their 3-4-5 hitters were Aaron Rowand (who has a .662 OPS), Cody Ross (.746) and rookie Brandon Belt (.685 in limited action).

By acquiring Beltran, it doesn’t mean the Giants will get past the Braves — their first-round playoff opponent if the season ended today — or that they will get past the Phillies (who own by far the largest run differential in the league, at +103) in a possible NLCS. But it means they have given themselves every chance to do so.

Meantime, in Wheeler, the Mets get a 21-year-old flamethrower who was the sixth overall pick of the 2009 draft — someone they can envision pairing with top Mets prospect Matt Harvey atop their rotations in 2013 and beyond. Wheeler ranked 35th in Baseball America’s midseason list of the top 50 prospects in the game. No pitching prospect is a sure thing, however, and Wheeler’s high walk rate (5.2 per nine innings) in the minors should be a concern. But with a 97-mph fastball and good secondary pitches, he has swing-and-miss stuff (10.3 strikeouts per nine innings) and won’t even turn 22 until next May.

The Mets’ efforts to trade Beltran were initially seen as a means of dumping salary (Beltran is owed about $7 million of his $18.5 million salary), perhaps in advance of an all-out blitz to re-sign sparkplug shortstop Jose Reyes. But in the end, the Mets, who are believed to be paying a significant portion of Beltran’s remaining salary by sending cash to the Giants in the deal, chose the better prospect over the better financial deal.

And the Giants, unlike their top competitors, chose to mortgage a piece of their future for the chance to win now.