you are lucky you stopped it before anything actually happened.
Not long after we got Harlow, she and Degan got into it. (She is always the perpetrator in any 'arguments' they have), but this one was pretty bad. There were four guys in our living room when it happened and no one stopped them! I don't know what they were fighting over, but when I yelled at them to stop Degan went running and Harlow kept after him. I had to run from the other room and break them up. Harlow had a pretty deep puncture right on her forehead from Degan's tooth, and also one on the side of her head. It was really scary, I yelled at our friends who just watched it happen, and had to call the emergency vet. Luckily the wound healed without any stitches or anything. We actually considered getting rid of Harlow. We told ourselves if anything like that happened again she would go. Fortunately, their listening skills have improved since then, and Harlow is much less defensive. (I think because she was a starving stray as a puppy she had always been extremely territorial.) Also, we are a lot less tolerant. When they play they are VERY vocal. Never aggressive, but they play pretty rough (typical pits) and we have learned what signals they give if it is taken too far, and we immediately break it up.
We never leave them together if we leave the house, and don't really leave anyone else to watch both of them, just in case.
Hopefully one of yours was just grumpy and they will go back to being best friends again