If it was for the division championship they would rank the teams based on head-to-head results. The lower ranked of the two teams would play first and the winner of that game would play the highest seeded team for the division championship. If the teams had identical records against one another they would use the following tie-breakers (they play 19 games for each series, so it would have to be a rock-paper-scissors type scenario, something like where each team was 10-9 and 9-10 against the other two)... Here are all of the gory details if you would like, How to determine playoff tiebreakers