We investigate production of fermionic dark matter χ via pp → pγp → pjχχX mediated by a leptophobic spin-1 particle, where one of the protons remains intact and is tagged by forward detectors. We find that the masses of χ and Y are severely constrained when Y interacts with χ and quarks through the vector couplings. We show that the dark matter search in this production channel has sensitivity for the mediator mass m Y 1.4 TeV at the 14 TeV LHC with the integrated luminosity L int = 3000 fb −1 . The lower mass bound on the dark matter is m χ 550 GeV at the mediator mass m Y = 1.2 TeV.