I'm not sure but I think they do use the combined.
https://www.mlb.com/news/mlb-playoff-tiebreaker-rules
It's more complex for three-team ties.
If the three clubs DO NOT all have identical records against one another and Team X has a better record against Teams Y and Z, then Team X is the qualifier. If Team X and Y have identical records against one another and each has a better record against Team Z, then Teams X and Y follow the two-club tiebreaker rules to determine the qualifier. Otherwise, the three clubs are ranked by their overall winning percentage against one another, and the club with the highest overall winning percentage is the qualifier. If two of the clubs have identical winning percentages in this scenario, then they would follow the two-club tiebreaker procedure.