Alessandra Ambrosio’s love game is strong, and she’s showing it -- the model was all about that PDA with her BF Buck Palmer during a sun-soaked beach day in Brazil.

The catwalk queen was turning up the heat in a tiny green bikini, flaunting that jaw-dropping figure and taking breaks from her beach fun to lock lips with her fashion designer beau.

Alessandra wasn’t shy about showing who’s hers ... 'cause she was all over Buck, wrapping herself around him, kissing his back, and making it crystal clear -- this man’s off the market.

In between the canoodling, the two played a bit of beach tennis, snacked, and soaked in the beach vibes.

Alessandra’s obviously in the honeymoon phase with Buck. They just went public in December, but she’s already cranked up the lovey-dovey dial -- way more PDA than we ever saw with her ex, Jamie Mazur, who she was engaged to for 10 years without ever making it to the altar.