Dixon overcame engine problems to win the 2013 IndyCar title by 27 points over Helio Castroneves, who came in sixth Saturday.
Dixon, who won championships in 2003 and 2008, gave Chip Ganassi Racing its fifth title in six seasons.
Power netted his third win of the season and 20th in his career. It was just his second career win on an oval.
The Fontana, Calif., track was the scene of a heartbreaking finish to the season for Power last year, when he finished 24th and lost the 2012 title to Ryan Hunter-Reay by just 3 points.
Ed Carpenter finished second, followed by Tony Kanaan and James Hinchcliffe.