The Day by Day Database now contains post-season batter and pitcher lines from 1969 to the present. That covers the era of multiple rounds in the playoffs. Mariano Rivera pitched pretty well in that time, and actually ranks tenth in innings. For batters with a minimum of 70 PA, Hanley Ramirez ranks first in batting average. I would not have guessed him. If one reduces the minimum to 50 PA, Fred Lynn pops to the top with a .407 BA, just beating out Billy Hatcher and Jose Offerman.