バルカン同盟
Peterson entered his rookie season in 2008 with Rilski Sportist who plays in the International Balkan League as well as the Bulgarian National League. He was awarded Most Valuable Player of the Balkan League in 2009 and was listed on Eurobasket.com as the Balkan League Import player of the year, Center of the year and Player of the year. He also led Rilski to the 2009 Balkan League Championship. He played with Rilski Sportist for two consecutive seasons (2008–2010), where he continued to dominate the league as the leading rebounder and finished 3rd in scoring. He was awarded MVP of the Balkan league for the second season in a row and led his team to a 2nd-place finish for the National Cup.