The Denver Broncos were supposed to try and win despite having Trevor Siemian as their starting quarterback. Siemian turned that on its head on Sunday.

In a huge test, at a tough Cincinnati Bengals team, Siemian was the star. Siemian, in his first road start, threw for 312 yards and four touchdowns in a 29-17 victory. The Broncos are 3-0 against the Carolina Panthers, Indianapolis Colts and Bengals, three pretty good teams.

Trevor Siemian threw for more than 300 yards and the Broncos improved to 3-0 (AP) More

It’s an incredible story. Never before had a defending champion entered the season with a starting quarterback who had zero career pass attempts. And this quarterback was a seventh-round pick who wasn’t very good at Northwestern, and had his senior season cut short with an ACL injury. Siemian has the pedigree of a quarterback you have to start if everyone else gets hurt. But the Broncos talked him up all offseason, he won the job in preseason, and he was fantastic in a big win Sunday.

The Broncos trailed in the fourth quarter before Siemian threw two touchdowns. One was a 1-yarder to tight end John Phillips to give the Broncos the lead. His touchdown to Demaryius Thomas wasn’t a game-manager type throw. He fired one deep to Thomas, who boxed out the cornerback and hauled in the 55-yard score. It was a great play by Siemian and Thomas. Siemian also had a nice 41-yard touchdown pass to Emmanuel Sanders.

Siemian was in a tough spot going into the season. Most fans didn’t know who he was until he got the starting job. He was replacing Peyton Manning, one of the legends of the game. He was coming in for a team that won a Super Bowl last year and wants to repeat. And on top of it all, he had a first-round pick, Paxton Lynch, waiting behind him. None of that has fazed him.

The story is playing out in an amazing way. Credit to general manager John Elway and the Broncos’ scouting staff for finding Siemian and picking him, and to coach Gary Kubiak for putting him in positions to succeed.

One of the wildest stories in the NFL marches on. The Broncos are perfect, and they’re not exactly carrying Siemian along for the ride. Siemian was the biggest reason they beat the Bengals on Sunday.

– – – – – – –

Frank Schwab is the editor of Shutdown Corner on Yahoo Sports. Have a tip? Email him at shutdown.corner@yahoo.com or follow him on Twitter!

Follow @YahooSchwab