Here's a neat little trick, if you are being chased down, go somewhere only accessible by vaulting, for example, this fire escape. When they come through, they will be caught in the animation as they get shot. Easy kills.
In this case my partner and I had dropped El Pozo, and we were looting for a while, until my partner was killed by these guys. I was close by, and tried to get a few shots off, but had poor positioning. So I went someplace where I had the advantage. I ran into this apartment, up the stairs, and onto the fire escape. They knew I was in the apartment somewhere, so they swept the whole building, until there was one more place, the roof. I listened as they approached, on the other side of the wall. I primed my weapon, and shot them like sitting ducks.