ST. LOUIS – It would have been remembered as a defining moment for this Steelers defense, the game when it may have turned a corner from a unit that had to be overcome to one capable of being the difference between winning and losing. It would have been remembered as the day the Steelers defense did not allow a touchdown AND authored the takeaway that ultimately swung the game in their favor AND closed it out by turning the ball over on downs with an incomplete pass with just over one minute remaining.

Instead, it will be remembered as the day Ben Roethlisberger injured his left knee.

As this is being written, the Steelers have no definitive word on the severity of Roethlisberger's injury, but the feeling is it's going to be a question of how bad it is as opposed to whether it's bad or not. If the ACL is torn, it's a season-ender. If not, well, then it comes down to how much time Roethlisberger will miss, a calculation almost no one can believe will be less than a month.

All of this is to be digested in the immediate aftermath of the Steelers' 12-6 victory over the St. Louis Rams yesterday, a win that served as both their second in a row on the young season and their first on the road in 2015. In those very specific ways, it was a very productive day for the Steelers inside an Edward Jones Dome that sure seemed to contain more Terrible Towels than fans rooting for the home team.

If only Roethlisberger hadn't injured a knee.

The 2015 Steelers are a team built like no other in franchise history in that the offense was expected to do most, if not all, of the heavy lifting. Back in the late 1970s, the Steelers won a couple of Super Bowls behind an offense that was the first to take full advantage of new rules implemented following the 1977 season to neuter their own defense, which had been judged by the NFL to be too dominating for the league's own good. But even those Steelers offenses – led by Terry Bradshaw, Franco Harris, Lynn Swann, and John Stallworth – were complemented by a defense that while somewhat neutered by the rules changes still had four first-ballot Hall of Fame players in the starting lineup.

This edition of the Pittsburgh Steelers has nothing close to a comparable level of defensive talent as those late 1970s teams, but with the way the game now is officiated at the professional level it's more important to be great on offense. The 2015 Steelers seemed to be on the way to fulfilling their potential for greatness, and so it seemed to be left to the defense to just not screw it up.

Against the Rams, the defense was on the polar opposite end of the spectrum in terms of the don't-screw-it-up mandate. Again, no touchdowns allowed, including a stand on a St. Louis possession that included a first-and-goal at the 7-yard line and ultimately ended with a 27-yard field goal. The Rams were 2-for-10 on third downs and 0-for-2 on fourth downs. They finished with 258 total net yards, including 71 yards rushing. The Steelers defense had four tackles for loss on Rams' running plays, two sacks of quarterback Nick Foles, and during a second half played largely without Roethlisberger the St. Louis offense barely managed to split the time of possession evenly.

The hero was Will Allen, he of the fourth quarter interception but also the guy whose open field tackle of Tavon Austin on a third-and-6 in the first half led to a fourth down and a fake punt that didn't work. But in addition to Allen, there were so many others whose contributions were significant to the victory. Just plucking names off the final statistics tally, Stephon Tuitt, Lawrence Timmons, Will Gay, and Arthur Moats. But then there were others who flashed with a contribution at a critical moment, such as Sean Spence's tackle for loss during that stand beginning with the first-and-goal from the 7-yard line, and Ross Cockrell's pass defensed on a third down after the Rams looked like they were about to move the ball into scoring territory. Certainly there had to be others, and their accolades might only come in the relative privacy of a team meeting, but in the overview of the afternoon it can be said the Steelers needed a lift after their quarterback was lost to a knee injury and their defense was up to the challenge.

What happens from now will reveal whether this was a turning point for this young and still developing Steelers defense, whether the game's final three minutes – when the defense took the ball away to set up the insurance field goal and then turned the ball over on downs to secure the victory – will turn out to be a turning point for this team this season.

Pending the results of an MRI.