Keselowski, who drives for Penske in the Sprint Cup series as well, finished third at Texas Motor Speedway, adding enough points to his tally in order to win the second-tier series title with two races still to run.
Although Penske has won multiple championships in almost every form of racing he has entered in the US, he had never won a NASCAR title before, coming closest back in 1993 with Rusty Wallace finishing second in the Winston Cup to the late Dale Earnhardt.
"Obviously Roger has some major accomplishments, but never a NASCAR title, and you sit back and say 'why not?'," said Keselowski, who is in his third full Nationwide season and his first for Penske after driving for Dale Earnhardt Jr's team until last year.
"Coming to Penske, I told Roger that I wanted to do this Nationwide deal and he looked at me like I was crazy. 'Why would you want to do that? It takes the focus away from the Cup side!' I explained to him that we're building a foundation for success at Cup level and it's here at the Nationwide level.
"It's here that we're building people, cars, attracting sponsors and doing things that will make the company stronger as a whole, and give it a better shot at winning a Cup championship. Winning a championship today is kind of a way to look at Roger and say 'this is what I'm talking about!'."
Keselowski has won six races this season, half the number achieved by last year's champion Kyle Busch, who was not running in the series full-time.
The Michigan-native has one Cup win to his name, which he achieved last year at Talladega while driving for Phoenix Racing.
Danica Patrick took part in Saturday's Nationwide race at Texas, her 11th outing in the series, finishing 22nd and three laps down on event winner Carl Edwards.
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