Ryan Reynolds and Sandra Bullock star in “The Proposal.”

Sandra Bullock may be aging out of the years when Hollywood sees her as Miss Congeniality, but not without one last fling. “The Proposal” has her playing the icy boss who blackmails her younger assistant into a sham marriage to save her Green Card.

It’s a performance with real comic juice, a woman acting her age and matched by a co-star whose comic timing complements her own — the very face of big-screen sarcasm, Ryan Reynolds.

And if she has held out until she’s 44 to deliver her first-ever honest-to-Keanu nude scene, honey, it was worth the wait.

Margaret Tate is a book publisher, a humorless martinet whose staff quakes in her presence and e-mails warnings about her every move. (“The witch is on her broom.”)

She gives as good as she gets. Her put downs are half-whispered asides that everyone hears, especially her long-suffering assistant, Drew (Reynolds), who can’t let on that he’s just had to make a personal call to cancel a trip to his granny’s 90th birthday because of work.

“That your family?”

“Yes.”

“They tell you to quit?”

“Every single day.”

But she’s Canadian, and she has ignored the warnings about her status. Just as she’s about to become queen of all she surveys at her firm, deportation awaits. She lies on the fly, tells the boss that she’s about to get married and names poor Drew, whom she knows nothing about, as the lucky fella. The catch — it’s not just the boss they must fool. Immigration is leery of such sudden nuptials. They’ve seen “Green Card,” too.

They’re off to “get to know” each other and tell Drew’s family the happy news. They live in Alaska and Ma and Pa (Craig T. Nelson and Mary Steenburgen) are not what you’d expect, especially not Granny (Betty White, a hoot as always).

Director Anne Fletcher (“27 Dresses”) doesn’t serve up many surprises, but she lets her practiced cast go through their paces, and that’s almost enough. The finale flounders after the fun that came before.

Bullock’s longtime fans should be happy to see her fully engaged in a role that suits her and paired, at last, with her comic equal: Reynolds.

Maybe there’s a Diane Keaton future for her in mature romances, or maybe this is Sandy’s last best shot. But dressed to the nines or naked as a jaybird, there’s nothing indecent about her in “Proposal.”