It turns out that Mayor Bloomberg, who made a big show of spreading his love around in the 2010 election cycle to demonstrate he dedication to post-partisan politics, quietly chose sides in the battle for control of the state Senate, after all.

And he bet well.

The billionaire mayor gave at least $500,000 to the Senate GOP’s housekeeping committee, according to a source familiar with Bloomberg’s largesse. Another source pegged the final amount from the mayor to the Republicans at just under $1 million.

It’s a little hard to peg down the exact amount at this point because the party housekeeping accounts, which have no contribution limits and are thus the favored vehicles of deep-pocketed donors, are not required to file its next report until the middle of next month.

Deputy Mayor Howard Wolfson declined to comment, although he did not dispute that Bloomberg gave big bucks to the Senate Republicans during this campaign.

Sen. Marty Golden, who, along with outgoing Sen. Frank Padavan, is arguably closest to Bloomberg than any other GOP conference member, professed complete and total ignorance about the mayor’s contribution(s).

Officially speaking, Bloomberg personally helped candidates who had been or would be helpful to NYC. That included Padavan, a longtime Bloomberg ally, and Bob Cohen – both of whom lost their respective races. (Padavan was toppled by a veteran Bloomberg critic and would-be 2009 mayoral opponent, former NYC Councilman Tony Avella).

Bloomberg also backed and/or raised campaign cash for a few Senate Democrats, including Sen. Craig Johnson, who has all but lost his fight against his GOP opponent, Jack Martins; and soon-to-be-former Assembylman/Senator-elect Adriano Espaillat, who is about to assume AG-elect Eric Schneiderman’s seat.

Bloomberg used to be the Senate Republicans’ largest single donor. But his last big check came in 2008 ($500,000 to the housekeeping account). That time, the mayor bet badly, as the Democrats won a narrow, two-seat majority.

Bloomberg’s continued support of the GOP did not win his friends in the Democratic conference. That sowed the seeds for a number of policy battles, the biggest of which was over the re-approval of mayoral control – a fight the mayor eventually won.

The mayor has had a rocky histroy in Albany, seeing some of his signature legacy projects die at the hands of legislative leaders, including the West Side stadium and congrestion pricing.

(Assembly Speaker Sheldon Silver played a big role in both of those losses, although the fact that then-Senate Majority Leader Joe Bruno, a Bloomberg ally, also voted “no” on the stadium is often overlooked).

Between the GOP’s likely return to power in the Senate and the ascent of Governor-elect Andrew Cuomo, whom Bloomberg endorsed this fall, the mayor’s relationship with Albany is poised to improve considerably come 2011.