Ryan Gosling and Eva Mendes act sly at 'The Place Beyond the Pines' premiere

Ryan Gosling and Eva Mendes are experts at keeping their relationship under wraps.

The supremely private couple didn’t even let their guards down inside the after-party for the premiere of their flick “The Place Beyond the Pines” in NYC on Thursday night.

The on- and off-screen pair — who started dating more than a year ago — mingled separately at the party, held at the Bowery Hotel, a partygoer told us.

“They actually kept things very professional and didn’t speak once,” the partygoer said of Gosling, 32, and Mendes, 39, who arrived separately at the Svedka-sponsored bash.

“They both mingled and worked the room,” the spy added.

They didn’t pose alone together earlier in the night, either, at the movie’s premiere at the Landmark Sunshine theater.

Gosling, looking dapper in a velvet Gucci suit, and Mendes, stunning in peach Prada, posed separately and for a few photos with co-star Bradley Cooper.