<prompt> Lapho kugqashuka iMpi Yezwe I ngo-1914, uPetrović wayephethe amabutho ayeqaphe isiteshi sesitimela esikhulu saseBelgrade. NgoNovemba nangoDisemba 1914, ngesikhathi sokuhlaselwa kwesithathu kwe-Austro-Hungary eSerbia, uPetrović wayeyisikhulu esiphezulu endlunkulu ye-First Army eyayiholwa ngu Armijski đeneral uLieutenant General Živojin Mišić. Ngesikhathi sakhe kulesi sikhundla, i-First Army yalwa neMpi yaseKolubara  <response>: , kwaba ukunqoba okunqumayo kwamaSerbia. Ngo-1915, u-Petrović wayengumsizi wezikhulu ezindlunkulu ze-Infantry Division Timočka, futhi wakhushulelwa esikhundleni sokuba yi- potpukovnik u-lieutenant colonel. Phakathi kukaDisemba 1915 noFebhuwari 1916, ngemuva kokuhoxa isikhathi eside kweRoyal Serbian Army eMontenegro, wayala ikamu lezempi eValona e-Albania. NgoFebhuwari 10, 1916, iRoyal Serbian Army yayisishiye i-Albania yaya esiqhingini saseGrisi iCorfu, futhi lapho yahlangana kabusha. 