Suisham's boot allowed Pittsburgh to build on their advantage with a field goal, although Baltimore chipped away at the lead thanks to a pair of Justin Tucker field goals of their own just before the break.
Defensive toughness reigned supreme in a tight third start to the second half, with Suisham the only scorer as his 28-yard field goal edged the Steelers 13-6 ahead.
Tucker and Suisham then traded field goals early in the fourth quarter before Baltimore roared back to set up a thrilling conclusion.
Pittsburgh thought that they had snatched victory with a fine solo run the length of the field, but the referee judged the effort out of bounds to force the hosts into a rethink.
With time running out, Roethlisberger regrouped and got into field-goal range, allowing Suisham to kick the winning 42-yard field goal with just three seconds remaining.