You should not be surprised by how well the NFL's best defense played against one of the NFL's most efficient offenses. The Bears prevailed 15-6 in a game that felt more like a three-touchdown blowout. Chicago's defense held the Rams to 214 yards -- and just 98 in the first half -- didn't allow a touchdown to a team that hadn't scored fewer than 23 points in a game this season, and held the Rams' offense to 3.5 yards per play -- half of what they averaged coming into Sunday night.

It also marked the return of Mitchell Trubisky, and that could mean a great deal to the Bears' hopes of a deep playoff run.

Trubisky returns to mixed reviews

This was Trubisky's first game since Week 11 when he suffered a right-shoulder injury late against the Vikings. The timing couldn't have been worse, as the second-year quarterback was coming off his most consistent stretch of the season. In Week 9, the Bears cruised to a 34-22 victory over the Lions and Trubisky finished 23 of 30 for 355 yards and three touchdowns. In that game he was smart and efficient, and he looked every bit the franchise quarterback the Bears envisioned when they selected him second overall in the 2017 NFL Draft.

A week later against the Vikings, Trubisky didn't put up the numbers we saw against Detroit, but this was his second-best effort of the year. It was a milestone of sorts, because other than his six-touchdown performance against the Buccaneers in Week 4, there were plenty of reasons to wonder if he'd ever grow into the role. Trubisky over the first two months of the season too often looked to pull the ball down and run, too impatient to stay in the pocket to let the routes unfold in front of him. But first-year coach Matt Nagy, who spent 10 years on Andy Reid's staff, never wavered; he knew this would be a process, and it appears we're starting to see the glimpses of what Trubisky can become. "He's slowly improving, which I love," Nagy said after the Lions win. "It's not going to be an overnight thing; he had a good game and we want to continue to have those good games. But there's a process to it."

And then Trubisky was injured against the Vikings. He didn't touch a football for 10 days, stood on the sidelines as Chase Daniel started the predictable Thanksgiving win against the Lions and the inexplicable 30-27 overtime loss to the Giants. Now, three weeks later, Trubisky is back on the field and looks a lot like the quarterback we saw over the first seven or eight weeks.

Trubisky missed wide open receivers from the start. He airmailed Josh Bellamy on the first drive and gave Marcus Peters the easiest interception he'll likely ever have:

And then, while trying to drive the Bears into field goal range at the end of the half, he woefully underthrew Taylor Gabriel near the sidelines:

Again, the Bears' defense bailed Trubisky out, stifling any offense the Rams might try to muster, and the teams went into the break, tied 6-6.

And whatever defensive coordinator Vic Fangio told his unit while they loaded up on orange slices, it must've stuck. Chicago's defense came out and stuffed Gurley for a five-yard loss. They followed that negative play up with this negative play:

Nagy appeared to simplify things for Trubisky too. He threw confidently on his first two attempts of the second half, and both went for first downs. That confidence got the Rams' attention and, as a consequence, opened things up in the running game. We saw glimpses of that in the first half with Tarik Cohen:

But it was taken up several notches after the break. Cohen ripped off a 23-yard run, and Trubisky followed that up with an eight-yard pass that took the Bears down to the Rams' 2-yard line. And then things got wild:

That's right, a big-fella touchdown, courtesy of tackle Bradley Sowell.

But Rusty Trubisky didn't stay in the locker room at the half; he was on the field for the Bears' second series and made another terribly inaccurate throw -- right to the Rams. The score was 15-6 at the time, and Los Angeles was in Chicago territory poised to make a move. That lasted all of five seconds because Goff out-Trubisky'd Trubisky on the very next play:

But in the fourth quarter, the Rams finally were able to string together a drive. Fourteen plays and 5:21 later, Chicago held firm, L.A. was forced to attempt a field goal ... and Greg Zuerlein doinked it off the right upright. The Bears maintained that nine-point lead with 10 minutes to go.

The Rams got the ball back four minutes later and, well, that blip of offensive football on the previous drive? Turns out that was an aberration. They ran seven plays for just eight yards, including a fourth-and-4 sack courtesy of Akiem Hicks.

The Rams got the ball back two minutes later and that drive ended like three of the 12 before it: with a Bears interception (more on that below).

As for Trubisky, he has a long way to go as a pure passer. This isn't some great secret. But when you factor in the Bears' defense and Nagy's ability to dial up the right plays in spite of Trubisky's inexperience, Chicago is basically running the offense the Ravens are striving for with Lamar Jackson. Right now, the Bears are doing it better, in part because their defense allows them to get away with some growing pains.

This Bears defense is terrifying

Here was the big question coming into this game: Could the Bears stop the Rams' stretch zone? Because just about everything L.A. does successfully on offense is a function of the stretch zone. It starts with Gurley and the running game, obviously, but extends to many of the throws Goff makes downfield, as well as the bootlegs and roll-outs.

To answer the question, consider this: Gurley finished with 11 carries for 28 yards -- that's 2.5 yards per carry -- and Goff was an abysmal 20 of 43 for 180 yards (4.1 YPA!), no scores and four interceptions. Yes, one came on a Hail Mary at the end of the first half, but the other three were all on Goff.

Here's No. 1:

Now you could make the case that left tackle Andrew Whitworth stepped on Goff's plant foot as he attempted to follow throw. Fair enough. But where was Goff going with that pass even if he had an unobstructed view?

Goff's second pick came at the end of the first half on what amounted to a Hail Mary. Here's No. 3:

We mentioned it in the section above, but the point remains: Trubisky had just uncorked an interception and the Rams had a chance, in Chicago territory, to finally get something going. Nope. Kyle Fuller undercut the throw and gave the ball right back to the offense.

And here's No. 4, which put the finishing touches on an forgettable evening:

And for as clinical as Goff has been for much of this season, he looked like the wide-eyed rookie who struggled during his 2016 rookie campaign. This is more than likely a function of the competition and not so much a reflection of Goff reverting to his time under Jeff Fisher. Either way, the Rams don't resemble the team from earlier this season that jumped out to an 8-0 start and appeared unbeatable. Instead, the Bears have provided a blueprint for slowing them down: stop Gurley and make the offense one-dimensional.

That's easy for us to say but it's been nearly impossible to execute for every team on the Rams' schedule except the Bears. We know this defense is already the best in the NFL, but how they perform over the next month could determine if we're talking about them in the same breath as the 2008 Steelers, the 2000 Ravens and, yes, the '85 Bears.

What's next

The Rams (11-2) are now the No. 2 seed in the NFC, behind the Saints, and have regular season games left against Philadelphia, at Arizona and against San Francisco. The Bears (9-4), who remain the No. 3 seed, have games against Green Bay, at San Francisco and at Minnesota. You can watch both teams' Week 15 games on fuboTV (Try for free).

Relive all the action from the game in our live blog below.