Fighting almost exclusively in Spain for the next decade, Petrov received his first world championship opportunity on 23 September 2011, when he faced WBA (Regular) super-lightweight champion Marcos Maidana.

[2] Throughout 2014, Petrov fought in the United States for the first time and participated in ESPN's Boxcino lightweight tournament, as part of their Friday Night Fights series.

He won his quarter- and semi-final matches against Fedor Papazov (six-round unanimous decision on 21 February) and Chris Rudd (fourth-round stoppage on 28 March), and the tournament final on 23 May by stopping Fernando Carcamo in eight rounds.

On 30 September 2016, Petrov dominated Michael Pérez in bloody fashion to force a corner stoppage in the sixth round, which earned him a mandatory opportunity for both the WBA and WBO lightweight world titles.

[4][5] On 23 January 2017, promoter Frank Warren confirmed that Petrov would face WBO lightweight champion Terry Flanagan on 8 April, in Manchester.