Padilla, a former state senator, won with 53.6% of the vote.
His campaign reported Monday that it spent $3.8 million.
Peterson, a Santa Monica resident, reported spending $506,600 on his campaign, including about $12,000 he lent the effort from his own pocket. He spent much of his money on radio ads.
Peterson is executive director of the Davenport Institute for Public Engagement and Civic Leadership at Pepperdine University.