Petrosian achieved his grandmaster title by scoring norms at the under 18 World Championship in 2002, the Batumi Open in 2003, and the Aeroflot Open in Moscow in 2004. In the same year he tied for 2nd-3rd with Zhao Jun in the World Junior Chess Championship in Kochi, India. In 2005, he tied for first in Tehran, Kish and Lausanne; in 2006 tied for first in Lyon and Dubai; in 2008 tied for first in Wheeling, Illinois and Las Vegas. In the same year he won a team gold medal (together with Levon Aronian, Vladimir Akopian, Gabriel Sargissian and Artashes Minasian) at the 38th Chess Olympiad in Dresden. In 2011, Petrosian tied for 1st–3rd with Marat Dzhumaev and Anton Filippov in the Georgy Agzamov Memorial in Tashkent and won the event on tie-break. In the same year he won the first Armenian Chess960 Championship, tied for 2nd–4th with Abhijeet Gupta and Magesh Panchanathan in the third Orissa International GM Open Chess Tournament and came first in the 31st Villa de Benasque Open. In January 2012 Petrosian won the Armenian Chess Championship and in February 2012 came first in the Armenian Rapid Championship. In January 2013 he won the Armenian Chess Championship for the second time. He also won clear first prize in International "Grand Europe Open Albena-2013" in Bulgaria. In 2017 he finished clear first in the 45th Annual World Open at Philadelphia.