After fighting and running around for about 10mins trying to take this guy down I figured why not try a grenade, and well it worked a bit too well for how far you are in the game at this point imo.
Playing this game on Hard and near the end you come to this section and luckily this isn't the first time you will meet these guys so you have a good idea how to take them down. These ones however recover quicker so you need to be quick and close to get that fatal blow in.