That opponent, the Arizona Cardinals, quickly discovered the type of potential Garoppolo possesses, as he threw for 264 yards and one touchdown while completing 73 percent of his passes. He also led a last-minute drive to set up the Patriots' game-winning field goal.
It might feel like it's been awhile since that 2016 season opener, but Arizona coach Bruce Arians vividly recalled one particular thing about Garoppolo in that game on Wednesday morning.
"His poise," Arians said. "It was the opening game. A big, big game on Sunday night. His accuracy was really good in that game. But I was really impressed with his poise."
Although both Niners coach Kyle Shanahan and general manager John Lynch have repeatedly said this week that Garoppolo won't start Sunday against Arizona, Arians is preparing to face him just in case, lest he be caught off-guard should the Niners be running an elaborate smokescreen.
But Arians shouldn't worry, for there's really no reason for the 49ers to start Garoppolo less than a week after sending a second-round pick to New England to acquire him.
On Wednesday, Shanahan reiterated his plan to evaluate Garoppolo's state of readiness on a week-to-week basis while keeping perspective on the overall goal of having him as the quarterback for the future.
"I can't promise you guys that he won't play this week," Shanahan said. "I can't promise you guys that he'll play this year. I know that we have a guy that we're excited about and I know has the ability to really help us and help this team in the future. That's what I mean by [saying] we didn't do this to just save this year. We did this because we feel this will improve our team and our organization. I'm not going to put someone out there who I don't think has a chance to be successful."
Most likely, Shanahan, Garoppolo and the Niners will find a happy medium between the two extremes of playing right away and not playing the rest of the year. The most logical scenario would have the Niners sit Garoppolo on Sunday and again next week against the New York Giants, then take the following bye week to get him up to speed and potentially have him make his debut against the Seattle Seahawks on Nov. 26.
There are multiple reasons why waiting makes the most sense for the Niners and Garoppolo.
First, as Shanahan pointed out, he's coming to a brand new offense after spending three and a half years in the same scheme. The next few weeks will be as much about unlearning what he did in New England as will be is about downloading a new playbook into his brain.
Although Garoppolo has earned a reputation for his intelligence, there's still a steep learning curve. He spent most of Tuesday night with quarterback coach Rich Scangarello and Shanahan immersing himself in the playbook. At his first practice as a Niner on Wednesday, Garoppolo wore a wristband on his left wrist with plays on it. It's something Shanahan doesn't usually like his quarterbacks doing but is necessary in this case.
Earlier this week, Garoppolo recalled what it was like coming from tiny Eastern Illinois, where he didn't even have a playbook, to the Patriots, where he was thrust into a situation with one of the most demanding coaching staffs in the league.
Garoppolo was able to learn enough in short order then to become Tom Brady's backup and start in his place when Brady was suspended. Still, this is a completely different offense, something Garoppolo can see from watching tape of it.
"Just seeing it on film, you know, watching it, trying to pick up certain things when we were in New England and use them," Garoppolo said. "I mean, it's a fun offense to run. It looks like it, at least. I'm excited to learn it, get the verbiage down and everything, get in the huddle with the guys. That’s what I’m really looking forward to, just meet my new teammates, meeting all the staff and everything like that. It's going to be a great experience. I'm looking forward to it.”
The other and perhaps biggest reason for not starting Garoppolo right away has nothing to do with him and everything to do with the cast around him. Put simply, the Niners are banged up on offense. They lost left tackle Joe Staley to a fractured orbital bone last week, and he's not expected to return until after the bye at the earliest. Right tackle Trent Brown is working his way back from a concussion, and Garry Gilliam, Brown's backup, is out for the year with a knee injury. On top of that, receiver Pierre Garcon is battling a neck injury.
It's one thing to let rookie C.J. Beathard attempt to push through with a patchwork group around him. It's another thing entirely when it's your potential franchise quarterback.
Despite all of that, Shanahan indicated that Garoppolo will be Beathard's backup this week, meaning he's only a play away from entering the game. Because of all those injuries, the Niners simply don't have the luxury of carrying a third quarterback right now, so they can have needed depth at other spots.
"I think it's contingent on everything," Shanahan said. "I want Jimmy to have a chance to go out there and be successful. I don't expect anyone to fully understand it unless you've been in that situation before. But coming in and just learning completely new terminology is a big deal. You guys asked Jimmy to compare it to college to now; terminology-wise, it's always going to be a foreign language when you change what everything is called. ... We've got to work and figure out the best way to get our team ready. But one thing I know is I'm very excited to have Jimmy here and I'm looking forward to the chance when he does get his opportunity to play for us."
Considering the 49ers' consistent insistence on taking the long view, it would be a surprise if they suddenly decided to be short-sighted.