St Louis come into the playoffs on the back of a defeat, but having finished second in the standings with a 6-4 record.
The Battlehawks kicked off the campaign with a 16-10 win over defending champions DC, and then bounced back from a 31-15 loss at Dallas with a 34-30 success against Birmingham.
That was followed by a 28-22 defeat in DC, but they responded with their best run of the season as they won road games in Orlando, 25-17, and Louisville, 16-3.
St Louis then made it three-in-a-row with a 31-20 victory over Columbus, only to fall 23-16 at home to Houston a week later.
The Battlehawks avenged that loss the following weekend as they beat the Gamblers on the road, 21-15, but they failed to make it back-to-back wins as they fell Dallas, 20-16, last time out.