Wins, Losses and Saves are possibly the most arbitrary statistics in all of baseball. At times, wins are given to pitchers who had poor games, but were saved by their offense driving in high amounts of runs. Other times, pitchers throw gems, only to be penalized by their offense's poor output. And saves are given almost by simply showing up at the end of the game. None of these stats are tightly based on any sort of statistical analysis - they are given according to a set of rules that don't take the quality of the pitcher's performance into account.
Win Probability Added and Leverage Index, I believe, are possibly strong tools for awarding wins, losses and saves. While there are strong criticisms of the use of WPA and LI in aggregate, they are excellent at telling us how well a player did in a given situation or game, and how much that performance was worth. By analyzing how well a pitcher performed in a game we can properly dole out wins, losses and saves - these are single game awards.
The entire post is pretty long, so at this point I'll just direct you to my site where I put it up.