This is certainly a setback, but I wasn't hoping for 16-0, and 5-1 after six games is almost certainly a better start than anyone had predicted for the Lions.
Now the question turns to whether the Lions can rebound from this loss and learn from the game. The old Lions would lose one game and allow things to snowball on them.
Great teams aren't the ones who never lose. Great teams are the ones who always rebound and come back strong in the next game.
Which team are the Lions this year? We'll find out next Sunday.
And on that note, what did we learn from the Lions' first loss of the season?
And I'm not just saying that because the 49ers won. I wrote that slide headline when the Lions were leading by four.
This was, undeniably, a fantastic football game, played by a pair of tough football teams who could meet again in the playoffs. The storyline coming in was about two surprise teams trying to prove themselves as legitimate.
The mistake I made was in assuming that the winner would be considered the "legitimate" team. After watching this game, I'm convinced both teams are legit. But let's focus on the the 49ers, who should not only run away with the NFC West, but could be in the mix for a first-round bye.
I don't know exactly how this happened, but the 49ers' defense is far and away the toughest the Lions have had to face all season. Matthew Stafford was under pressure all day, Calvin Johnson failed to catch a touchdown for the first time all season, and the running game was its usual ineffective self.
The Lions' offensive line, on a related note, had their worst game of the season as well. Jeff Backus, in particular, came off decent games the Cowboys and Bears, only to have his lunch handed to him all day by Justin Smith.
All in all, the Lions just got beat. It doesn't mean they're done, by any means, and it doesn't mean the 49ers are far and away a better team. If these teams played each other 10 times, each team would likely win five.
But rather than get down on the Lions, give credit to the 49ers. They earned this win, and should earn many more as the season goes on.
The crowd noise last Monday night against the Chicago Bears was incredible, but I wasn't convinced.
The Bears have an awful offensive line, and the crowd surely got a boost from the Monday night atmosphere and the hated rivals on the field.
Then the Lions defense took the field in this game, and the 49ers started the game with more false starts (two) than offensive plays (one).
San Francisco is actually a good team with a good offensive line, so they reined in their false starts by the second half, but the crowd still had an effect on this game.
Alex Smith had to call timeouts at the line because he couldn't get plays off, and the 49ers' offense was never able to get an advantage with Ford Field booming all day.
That is, until it came down to crunch time. With the 49ers driving for what was ultimately the game-winning touchdown, the crowd seemed completely uninvested.
I'm as happy as anyone to see the crowd noise affect the game, but I would have rather the crowd cause that havoc on a potential game-winning drive. The Lions are learning how to be a winning team, so it's time Lions fans learn how to cheer for a winning team.
There's no doubt that the Lions' offense is loaded with playmakers.
But that doesn't make them anywhere near unstoppable, and the 49ers showed it this week.
The Lions were unable to convert for touchdowns in the red zone, Matthew Stafford looked completely out of sorts all day, and the team had another sub-par day running the ball.
The Lions have been playing a game of chicken with their ineffective running game all season, and they finally found themselves in a situation they couldn't pass themselves out of.
The defense did well to pick the team up after a bad offensive series, but they had something else to contend with...
Quick, does anyone know how far the 49ers had to drive for the game-winning touchdown?
It was 35 yards. Did the Lions turn the ball over? No, they punted 39 yards and gave up a 40-yard return.
Now, I feel bad making this call after the Lions shut Devin Hester down completely, but Ted Ginn Jr. slashed through with big returns all day, and that helped the offense, which had a difficult time against the Lions' defense, aside from a couple of big runs by Frank Gore.
I have no doubt that Matthew Stafford is a franchise quarterback.
Unfortunately, I also have no doubt that he has a ways to go yet.
In this game, Stafford took a safety, overthrew guys, underthrew guys, intentionally grounded the ball, and just generally looked like a talented guy with a lot to learn.
Stafford had two different opportunities to run a two-minute drill, and he failed to pick up so much as a first down either way.
Stafford was under a lot of pressure in this game, but many of Stafford's errors in this game had little to nothing to do with pressure.
Suffice to say, Stafford is still the second-best quarterback in the NFC North, but hopefully he uses this game as a learning experience.
The honeymoon is over. No more of this ridiculous 16-0 talk.
The Detroit Lions are 5-1, and the schedule is getting tougher. Now that the Lions have lost their first game, they re-join the pack of playoff hopefuls scrapping for every win they can get.
I say the season begins now because the winning streak is over. No longer is the debate going on about whether the Lions are the best team in the league, or the second or third-best. They're just a good team with positive numbers in both the win and loss column.
Now they need to prove the winning streak wasn't all momentum, and the fast start wasn't all smoke and mirrors.
The Atlanta Falcons come to town next week, and the Lions, as a good team, need to follow up their disappointing loss with a big win.