When you’ve already replaced a legend like Peyton Manning, stepping in for Sam Darnold doesn’t sound so daunting, which is perhaps why Trevor Siemian seemed so chill about making his first start in two years Monday night against the Browns at MetLife Stadium.

“Just do my job,” Siemian said of his expectations. “Run a clean operation and get the ball in the end zone. It’s pretty simple.”

Truth is nothing has been simple of late — not for Siemian and not for the Jets. Within a week they have blown a 16-0 lead to lose their season opener, lost wide receiver Quincy Enunwa for the season to a neck injury, sent their $52 million running back Le’Veon Bell for an MRI exam on his shoulder and diagnosed Darnold with mononucleosis.

That makes Siemian the starting quarterback, a role he once owned in 2016 when he was the Broncos’ top quarterback following Manning’s retirement. By 2017, Siemian was on the bench, due partly to injury, and was traded to Minnesota, where he spent the entire 2018 season watching from the sidelines as the backup to Kirk Cousins.

Still, he is 13-11 in 24 career starts and has a proven arm, having thrown for 5,686 yards and 30 touchdowns. Those aren’t bad numbers, especially for someone who was the last of seven quarterbacks taken in the 2015 draft as the 250th-overall pick. He signed a one-year deal with the Jets for $2 million to be Darnold’s backup, but now has a chance to jump-start his career.

“No player wants to bounce around and play for a bunch of teams,” Siemian said. “But on the positive side, you get to see different players, good players, good coaches, and what makes them so good. We’re all a combination of our experiences. We’ll see what works and go from there.”

Siemian has always shown enough potential to catch a coach’s eye. Then-Broncos coach Gary Kubiak had this to say in 2015: “There’s just something about the way he played, his footwork, his release. I liked the way he went about things.”

This was Jets coach Adam Gase on Thursday: “After Peyton left, I kept seeing him play a lot, and in my head I kept saying, ‘Wow, this guy really throws a nice ball. He gets it out and it comes out clean.’ The more film I watched on him and when we started evaluating him, I really liked him.”

This is still Darnold’s team, and whenever he is strong enough to return as the starter, he will. But Siemian has a chance to remind the NFL that he is a rare commodity: a reliable quarterback who can make plays in this league. Who knows what a good showing as the Jets starter might earn him next year? He turns 28 in December and has a lot of football ahead of him.

“I’ve played, so I guess in a sense I’ve been there and I’ve done it a little bit,” Siemian said. “It’s been a while. But I’m champing at the bit to compete and be out there with the guys. I’m excited to play this week.”

Gase shouldn’t have to change the playbook with Siemian at the helm. His mobility could be a weapon. The offense figures to be more impacted if it loses Bell, who is likely to play after an MRI exam on his shoulder came out clean. But even that prospect didn’t seem to rattle Siemian.

“We’ve got so many talented players that I’m going to lean on,” he said, “Jamison [Crowder], Robby [Anderson], Ryan [Griffin] and everybody up front has a ton of experience. I’m fortunate in that sense. I can lean on these guys and it makes my job pretty simple.”

If only it were that simple.