In March 2013, he won the eight-man Haarlem Fight Night IV tournament in the Netherlands to be crowned the WMTA World Super Welterweight Champion.
He defeated Abdallah Mabel at the Ring Rules event in Milan, Italy, on January 30, 2009, a win that earned him a place on the Oktagon presents: It's Showtime 2009 card held on March 14, 2009, where he beat Arnaldo Silva via unanimous decision.
Petrosyan ended the year by facing one of Thailand's top middleweights in Saiyok Pumpanmuang at Janus Fight Night: Thai Boxe Last Challenge on November 7, 2009, in Padua, Italy, where he lost by unanimous decision after a three round affair.
After outpointing Vuyisile Colossa in Ko Samui, Thailand on January 20, 2010, he took another points win over Dzhabar Askerov at Oktagon presents: It's Showtime 2010 in Milan on March 13, 2010.
He then lost a decision to Marco Piqué in Palermo, Italy, on June 26, 2010[5][6] before going on to take part in the first season of the Enfusion reality television show in Ko Samui.
Going down as the co-main event of Oktagon 2011 in Milan on March 12, 2011, both men traded heavy shots in the first round but Petrosyan began to pull away in the second by utilizing sweeps.
[21] Petrosyan was then invited to compete in the Fight Code Dragon Series, a sixteen-man -72.5 kg/160 lb tournament held throughout Europe over the course of 2011, and he was entered into the competition at the quarter-final stage against eventual champion Yuri Bessmertny.
[28] He was able to bounce back with a dominant TKO of Djimé Coulibaly at the Yokkao Extreme 2012 supercard in Milan on January 21, 2012, dropping the Frenchman a total of four times in the first two rounds and forcing a referee stoppage.