If the AFC championship game comes down to quarterback Peyton Manning dueling against New England counterpart Tom Brady, Denver is going to lose. Brady owns Manning. The Broncos’ best shot of beating the Patriots rests on the tender left shoulder of cornerback Chris Harris. And he’s hurting. Big time.

Harris is the most valuable player on a team whose championship dream is built on defense. He’s the flypaper in the No-Fly Zone. Without Harris, who played a team-high 96.99 percent of the defensive snaps during the regular season, the Broncos’ swagger slowly begins to disappear, along with their ability to use the intimidating man-to-man coverage, from which their confidence flows.

The health of Harris is far more crucial to the Broncos’ chances of beating New England than the arm strength of Manning. Harris is the antidote to New England receiver Julian Edelman, who makes the Pats’ offense so dangerous on third down.

And how worried is Harris about his shoulder, ailing from a deep bone bruise suffered Jan. 3 in the final regular-season game against San Diego?

“That’s all I’m damned worried about,” Harris told me Sunday evening after the Broncos escaped with a 23-16 victory against injured Pittsburgh quarterback Ben Roethlisberger and the gritty Steelers.

In a happy Denver locker room, Harris wore a grimace. So I had to know the truth: Whose shoulder was more messed up? The right shoulder of Roethlisberger, who created intense debate about his health in the days before the game? Or the left shoulder of Harris, who admitted he was in so much discomfort he couldn’t really tackle or even play press coverage?

“My shoulder’s way worse than Ben’s,” Harris said. He laughed. Laughed until it hurt.

Then, Harris got serious. Real serious.

“I played with one arm the whole game,” Harris admitted.

From the first snap by Pittsburgh, when Harris was beaten deep by Markus Wheaton on a long pass that Roethlisberger misfired, the star 26-year-old cornerback was not himself. During the Steelers’ second offensive possession, Harris uncharacteristically gave Sammie Coates a 5-yard cushion on a third-down completion, then whiffed badly on the tackle.

Coates rambled 37 yards before being stopped. Harris walked to the Denver sideline and threw his helmet in disgust. He reluctantly surrendered his regular spot in Denver’s base defense to Bradley Roby. Harris participated in a reduced role, as the nickel cornerback.

How important is Harris to the Broncos? Let us count the ways.

During the regular season, Harris almost never left the field for the NFL’s No. 1-ranked defense. He participated in 1,063 defensive snaps and sat out only 33 plays. By comparison, all-pro linebacker Von Miller played 835 snaps, which translates to 14 fewer plays per game than Harris.

Against the Steelers, Harris was on the field for a season-low 75 percent of Denver’s defensive plays. His effectiveness was clearly compromised.

“I have to tip my hat to Roby, man,” Harris said. “He played all the snaps for me that I usually play, and he made a lot of plays for us. There’s not too much I could do.”

How to cover for Harris’ injury will be a big challenge for defensive coordinator Wade Phillips. Harris left a playoff game two years ago with a torn anterior cruciate, and the Broncos were never the same without their best cover corner, ultimately losing the Super Bowl to Seattle in ugly fashion.

“His shoulder has been bothering him,” Denver coach Gary Kubiak said Monday. “He went out there and gutted it up and played with one arm, in a lot of ways. Battled for our team. Hopefully, there is some improvement this week, just physically.”

Roethlisberger threw for 339 yards against Denver.

“We busted coverages. We did stupid things out there,” Harris said. “A lot of times, (Pittsburgh) got the yardage off our busted coverages.”

Roby has a great future in the NFL … as a safety. If Roby is forced to play on an island as a corner against New England, Brady could well pick him apart. Nobody preys on weaknesses better than the Patriots.

If Harris can play at anywhere near full capacity, the game against New England is a tossup. But struggle as he did against Pittsburgh, and the Broncos’ chance of beating the Patriots drops to maybe no better than 25 percent. That’s how essential Harris is to Denver.

“It’s two games, I’ve had to fight through this. It’s football, man,” said Harris, who again expects a diminished role against the Pats. “I’ve got to try to do the best I can to be me out there. But it’s very hard.”

Mark Kiszla: mkiszla@denverpost.com or @markkiszla