ENGLEWOOD, Colo. --Just after halftime against the Dallas Cowboys, Trevor Siemian made a little move that paid off in a big way and showed his continued progress as a pro quarterback.

With the Broncos facing third-and-6 on the third play of the third quarter last Sunday, Siemian prepared for a shotgun snap. Three receiving targets were bunched to his right; Demaryius Thomas was split out to the left.

Then he looked and saw the Cowboys aligned with three defenders set beyond the line to gain. Siemian calmly walked up to the offensive line and checked into a draw play.

Siemian handed the football to C.J. Anderson. Anderson got past the line of scrimmage, then sprinted to the right of Ron Leary and to the left of Menelik Watson, who got upfield and blocked Cowboys linebacker Sean Lee.

It was a check that launched a 15-play drive that put the Broncos in front by three scores -- a margin they maintained for the rest of the game. It also reminded Anderson of the quarterback from whom Siemian learned so much.

"The third-and-6 run check was something that [Peyton Manning] would have done," Anderson said. "He's definitely understanding the game a lot more."

Plays like that are signs of a maturing young quarterback. The more Siemian sees on the field, the better he reacts. Those plays are also part of why Head Coach Vance Joseph gives Siemian credit for the Broncos' league-leading third-down percentage.

"I think it's Trevor. It's decision-making and its ball placement. Third downs are strictly on the quarterback. You're seeing exotic pressures versus four-man rush zones," Joseph said. "He's been efficient and he's been smart with the football. I've been pleased with Trevor, with his whole game, not just third downs."

It's also important to remember that Siemian has made just 16 starts. Only now is he starting to reach the point where he's seen most of what opposing defenses can toss his way.

"He's a lot more focused as far as reps. There's not too much that he hasn't seen," Anderson said. "The things that he has seen, you can definitely see him go, 'Hey, I have seen them before,' and he puts us in the right position."

And now he's in position to take the next step -- and with 16 starts, he has a full season's worth of work to evaluate.

Through 16 starts, Siemian has an 87.0 quarterback rating and a 24-to-12 touchdown-to-interception ratio. Among Week 1 starting quarterbacks with at least 16 career starts, that rating for the first 16 starts ranks 10th, just ahead of some high draft picks such as Tennessee's Marcus Mariota (No. 2 overall in 2015), Carolina's Cam Newton (No. 1 overall in 2011) and Tampa Bay's Jameis Winston (No. 1 overall in 2015).

But this must be noted: The vast majority of the current starting quarterbacks who had better quarterback ratings in their first 16 starts also had outstanding running games to support them. Dallas' Dak Prescott, for example, had a 106.4 rating last year, but he benefitted from Ezekiel Elliott, who led the NFL in rushing. Pittsburgh's Ben Roethlisberger posted a 105.2 rating in his first 16 starts over the 2004 and 2005 seasons, but the Steelers leaned heavily on Duce Staley, Willie Parker and future Hall of Famer Jerome Bettis, who combined to average 125.1 yards per game during Roethlisberger's first 16 starts. It goes on like that, with the notable exceptions of Aaron Rodgers and Tom Brady.

For half of Siemian's first 16 starts, he didn't the same ground luxury of most of the quarterbacks who had better first-16 ratings, as Anderson missed Siemian's last eight starts in 2016 because of a torn meniscus. In Siemian's eight starts without Anderson, the Broncos averaged 74.9 rushing yards per game.

With Anderson in the backfield with Siemian, the Broncos have averaged 126.9 rushing yards per game. That has helped Siemian, whose rating in games with Anderson is 95.7 -- a figure that would vault him from 10th to fifth among those Week 1 starting quarterbacks. And for what it's worth, the Broncos are now 7-1 when they start together.

"We want to play complementary football," Siemian said Sunday.

Denver's success through the air set the table for the Cowboys' third-down coverage that led Siemian to check to the run. That's one aspect of "complementary football." Siemian's overall success with Anderson is another. With Siemian and the ground game clicking, the offense bursts with possibilities.