Major League Baseball focuses its rule making on creating a universe where there is competitive balance among the teams. This concept is the ‘agreed to’ holy grail in baseball administration and has been the goal of league executives for decades.  I was once asked to develop a metric for determining whether competitive balance existed.
I only had to look to the standings to develop such a metric. As this is baseball, nothing is perfect, but teams are ranked according to winning percentage. These percentages normally run from just under. 600 to just over. 400. This means that  of every five games played, teams will win two and lose two. This leaves the Fifth Game to determine where a team is ranked.

This game can be recognized by fans as the one where the outcome is in doubt until late in the game, which is determined by a clutch hit, an error, or some sort of event that determines the outcome. A properly designed roster has late inning specialists such as defensive players, pinch hitters, set up men and closers. Of course, a basestealer is today a luxury because of expanded pitching staffs.
The Twins/White Sox game June 18, 2013 was a Fifth Game. The White Sox tied the game at 5 in the top of the 8th but failed to get the hit that would put them ahead. The Twins, aided by a lead off walk, scored two in the bottom of the 8th on a clutch hit. The game could have gone either way.
Teams keep track of series won and lost and this is in recognition of Fifth Game Theory. Keep this is mind while you are watching your next game and figure out if you are lucky to be watching a Fifth Game or not. They’re the ones that keep my attention.