Due to the two-month strike, the owners tried to create an equitable solution. So on August 6, the owners decided to split the 1981 season into two halves, with the first-place teams from each half in each division (or a wild card team if the same club won both halves) meeting in a best-of-five divisional playoff series. The four survivors would then move on to the two best-of-five League Championship Series. It was the first time that Major League Baseball used a split-season format since 1892.

http://en.wikipedia.org/wiki/1981_Major_League_Baseball_strike

That was a terrible decision.

Ok...here is the answer per the wikipedia link!

On August 20, Major League Baseball revised the rules so that if a team won both halves of the season, it would face the second season runner-up instead.