HOMESTEAD, Fla. — Here’s a tweet for Brad Keselowski: NASCAR champion. Roger Penske must like the sound of that, too.

The kid who stole the show at the season-opening Daytona 500 ended the year under the biggest spotlight of them all Sunday, beating five-time champion Jimmie Johnson to deliver the first Sprint Cup championship to Penske Racing. His first act as champion? Sending a tweet, of course, from inside his car: ‘‘We did it!’’ with a picture of the celebration waiting for him.