Mullens connected on 16 of 22 passes for 262 yards and three touchdowns in the win. He posted a passer rating of 151.9 -- the highest passer rating for player making his NFL debut since 1990 (min. 20 attempts) and the eighth-highest rating this season, per NFL Research. It was the highest passer rating by a 49ers QB since the 157.1 Alex Smith posted on Oct. 29, 2012.
He also became only the second quarterback since 2000 to throw a TD pass on each of his team's first two possessions and was the first QB since Gus Frerotte in 1994 to complete passes to eight different players in the first half of a debut.
"You never know until you see someone," 49ers coach Kyle Shanahan said about Mullens. "He didn't surprise us in terms of, the game's not too big for Nick. He's very poised. He is always locked in. The guys, they respect him. He earned a lot of respect in the preseason, them watching him play. Both years, last year and this year. The way he handles himself in practice each week. He didn't really know for sure whether he was going to start today, until today, and just the way he handled the two days of long walkthroughs and stuff.
"He's a machine in there and I was happy for him."
Another person who was happy for him was Hall of Famer Brett Favre. During his time at Southern Miss, Mullens made a habit out of passing Favre's marks in the history books. Favre wished Mullens good luck before the game and made a congratulatory phone afterward.
"It was pretty cool, definitely an honor," Mullens said. "It's cool to see Southern Miss alumni stay in tune with the program and support each other. Definitely appreciative of that and definitely have the most respect for Brett. He just told me how proud of me he was."
The question now is whether Mullens will play again. C.J. Beathard's wrist injury limited him to a backup role Thursday, but he's expected to be healthy in time for next week's game against the New York Giants. Is Shanahan mulling over whether to play Mullens over Beathard based off Thursday's performance?
"We'll consider it," Shanahan said. "Definitely not thinking about that right now, but our whole team played very well. Nick definitely did. ... It's good to get a win today and hopefully it can lead to some others."
In all, it was a memorable performance for a NFL player who wasn't verified on Twitter until some point during the second half of Thursday's game. Mullens certainly earned his blue check mark.