DRAKE SERVING IT UP TO SERENA WILLIAMS

Here it is … proof Drake and Serena Williams are officially a thing — making out at a fancy Cincinnati restaurant Sunday night … and TMZ has the pics.

Hours after Serena dominated and won the WTA tournament in Cinci — with Drake in the crowd — the two hit up the uber-fancy Sotto restaurant in downtown for some hoity-toity Italian food (the porterhouse is $85).

The two had a private room in the back of the eatery — where they couldn’t keep their hands and lips off of each other … while several patrons watched.

People inside the restaurant tells TMZ the two were joined by 6 other people …and at one point ordered a round of tequila shots for the table.

There have been rumors about the two hookin’ up for months — ever since Drake was spotted cheering for Serena at Wimbledon — but now the pics confirm it … it’s game on.