Unfazed by a three-game layoff, Darnold played one of the best games of his young career and sparked the Jets to their first win, 24-22 over the Dallas Cowboys on Sunday at MetLife Stadium.
"When you're out for so long like I was, you realize this game is a privilege to play it," said Darnold, who passed for 338 yards and two touchdowns.
With a hard-plastic guard protecting his back and previously enlarged spleen, Darnold said he "took a couple of shots" in the game, but he wasn't worried about the possibility of his spleen rupturing. He was medically cleared only five days ago, five weeks after the diagnosis.
"It didn't affect me at all," he said. "The pads worked great. Super light and also protected me well."
Darnold was so wiped out by the mono -- he felt symptoms in the Jets' Week 1 loss -- that he did nothing for three weeks. Two weeks ago, he was cleared for light cardio -- stationary bike and long walks. He came close to playing last week, but he was denied by team doctors because his spleen was slightly enlarged.
Showing no rust, Darnold knew from the first play -- a 17-yard pass to Demaryius Thomas -- he was destined for a big day. The highlight was a 92-yard touchdown pass to Robby Anderson, the second-longest scoring pass in Jets history.
"Sam is a special player," running back Le'Veon Bell said. "You've got a guy in there who's able to make plays, get the ball down field and get everybody lined up perfectly, getting them out of the huddle -- a vocal leader. ... We've been missing that these last couple of weeks."
That's an understatement.
With Trevor Siemian (one start) and Luke Falk (two starts) at quarterback, the Jets' offense managed only one touchdown and averaged only 165 total yards per game. On Sunday, they produced three touchdowns and 383 total yards.
Falk played so poorly that he was released on Saturday. Head coach Adam Gase opted for the recently signed David Fales as his No. 2 quarterback.
Publicly, the Jets' coaches tried to downplay Darnold's return, with offensive coordinator Dowell Loggains saying last week, "Sam is not a magic wand." But, in a way, he was.
Gase was so happy to have Darnold back in the lineup that he kept calling pass plays later in the game, when running the ball and milking the clock might have been the conventional choice. The Jets nearly blew a 21-3 lead, stopping a two-point conversion in the final minute to preserve the win.
"There was a lot of good," Gase said of Darnold, whose lone mistake was a red zone interception in the third quarter. "His pocket movement creates a lot of opportunities, and our guys did a good job of moving with him."
By sliding in the pocket and buying time, Darnold allowed the downfield passing attack to develop. He posted a career-high seven completions on passes that traveled at least 15 yards in the air, according to ESPN Stats & Information research. His touchdown to Anderson traveled 40 air yards.
"It was awesome," Darnold said of the play. "The way the safety bit down on the run, I just knew I had to put it out there. Robby is one of the best, if not the best, at tracking the ball in the NFL. I knew I had to put it out there and he'd go out and catch it."
Anderson, a nonfactor in the first four games, finished with 125 yards on five catches. Fellow receiver Jamison Crowder led the team with six catches for 98 yards. All told, seven players caught at least one pass.
"It was amazing to have my brother back out there," Anderson said. "It makes a big difference."
The Jets were so inept during their four-game losing streak that it prompted a players-only meeting last Monday, as team leaders tried to prevent an offense-defense fracture. In a way, Darnold galvanized a team perhaps on the verge of turmoil.
"I felt good out there," he said. "It was good to hear the fans roar again and be out there on the field with my teammates. There's no better feeling."