MLB

MOST VALUABLE POSADA

ALEX RODRIGUEZ, who is merely having the best season of any right-handed Yankee batter since Joe DiMaggio’s 1937, crashed his major-league leading 46th homer last night, a solo blow into the upper deck that gave Chien-Ming Wang breathing room after nursing a 1-0 lead into the bottom of the sixth.

Wang, who has evolved into the club’s most identifiable ace since Ron Guidry worked wonders in The Bronx Is Burning Era, spun his third straight dandy, getting double-play grounders in each of his final three full innings of work in limiting the Mariners to one run on five hits over 71/3 innings to win his 17th game and keep pace with Josh Beckett for the major-league lead.

And yet, while the potential AL MVP and potential AL Cy Young winner each shined yet again on this simply sublime night for baseball at the Stadium, it was Jorge Posada who provided the impetus for the 12-3 victory that extended the Yankees’ wild-card lead over Seattle to two games.

It was Posada who gave the Yankees a 1-0 lead with a second-inning leadoff home run. It was Posada who made a nifty, short-hop reception of Hideki Matsui’s throw from left before slapping an equally adept quick tag at the plate on Adrian Beltre to preserve that 1-0 lead in the fifth, when Kenji Johjima’s base hit appeared destined to have tied the score with no one out.

It was a degree of difficulty play of 9.9 with a 9.9 on the execution scale, as well.

Last night, it was Posada proving himself to be indispensable; perhaps, even with Rodriguez threatening to challenge the AL home-run record for right-handed batters – 58, established by Jimmie Foxx in 1932 and equaled in 1938 by Hank Greenberg – the most indispensable Yankee on the roster.

It was Posada, again, even before he completed a 4-for-4 night with another home run in the eighth to bloat the final score; Posada taking charge on the field by stepping in to prevent Wang from continuing when his back stiffened up in the eighth after he’d sat on the bench through a half-hour, seven-run, bottom of the seventh.

“I was not going to let him pitch,” Posada said of Wang, lifted by Joe Torre at the catcher’s insistence after pitching coach Guidry had visited the mound. “He wasn’t ready to pitch that inning. He wasn’t loose.

“The two pitches he threw; he didn’t look right, so I told the dugout to come out. He’s too valuable. We can’t afford to lose him. I wasn’t going to risk it.”

Make no mistake. This was a vital victory for the Yankees, who’d not only lost three of their previous four since sweeping the Red Sox, but who’d gone only 9-11 since Aug. 14. And make no mistake about this, either – in his 11th year in Pinstripes and in his eighth season as the everyday receiver, the 36-year-old career Yankee is having a career year.

“Jorge has been a rock,” said Rodriguez, who left the game with a twisted ankle in the seventh. “Both at the plate and behind the plate.”

Before the game, after the Yankees posed for their official team picture, a photographer snapped a shot of Posada with Derek Jeter, Mariano Rivera and Andy Pettitte, the string quartet of the four World Series winners from 1998 to 2000. Jeter and Rivera soldier on. Pettitte has returned after a sabbatical in Houston. And Posada merely gets better.

He merely gets better, as in a .337 average that’s fourth in the AL to accompany his 18 homers and 80 RBIs. He merely gets better, as in the perhaps pivotal tag play at the plate. He merely gets better, as in placing Wang in his protective custody.

The talk this year has been about A-Rod’s ability to opt out and move on. Posada, too, is in the final year of his deal, also eligible to opt out of New York as a free agent.

There is no telling which man would create the more impossible hole to fill should he flee.

larry.brooks@nypost.com