ENGLEWOOD, Colo. — When the Broncos needed Case Keenum's best on Sunday against the Chargers, he delivered.

Denver struggled to move the ball for the majority of the first three quarters as Keenum posted quarterback ratings of 50.3, 66.7 and 70.1 in the first, second and third quarters, respectively.

The Chargers, to that point, had dominated time of possession (30:25 to 14:35) and total yards (382 to 161).

But with Keenum at the helm, the Broncos' offense moved the ball when it mattered most.

Beginning after Von Miller's interception with 3:55 to play in the third quarter, Keenum helped engineer scoring drives on three of the Broncos' last four possessions.

Two of those drives culminated in touchdowns, while the final, last-minute drive set up Brandon McManus' game-winning 34-yard field goal.

Keenum didn't attempt a pass on the first of three second-half scoring drives — Phillip Lindsay and Royce Freeman ran well enough that he didn't need to — but was effective throughout the fourth quarter.

He fired tight passes to Courtland Sutton for 39 yards, Emmanuel Sanders for 38 yards and again to Sutton for 30 more yards to help the Broncos complete their 12-point comeback. And that doesn't include a tight-window throw to Tim Patrick that was called back due to an offensive pass interference call.

Keenum went 8-for-12 with 146 yards and a 108.3 quarterback rating in the fourth quarter

And Keenum's late-game success isn't an outlier.

In three of the Broncos' four wins, they've required a game-winning drive. And Keenum's responded by raising his game. Against Seattle and Oakland — and in a near-comeback against the Rams — Keenum's fourth-quarter passer rating has been higher than his passer rating in the preceding three quarters.

"He likes the challenge of bringing our team back," Head Coach Vance Joseph said Monday. "I think the looks are cleaner from a defensive perspective. He's always been that way, from college to his NFL career. He's been a gamer. He's played his best football in the critical moments. Our team expects that from Case, and he's been good at it."

The Broncos, as a team, have found ways to exploit defenses during those time-crunched situations.

"It's so different for defenses when you're playing just normal football," Joseph said. "You get more looks. So when you're in a two-minute offense and you're going fast, the looks become a little clearer, because obviously you're going fast and they're in two-minute mode. So you get more four-man rush, more single-high [safety coverage], more shell [coverage]. It's really clean looks."

Through the first 11 weeks of the season, only Drew Brees, Deshaun Watson and Andy Dalton have more game-winning drives than Keenum among NFL quarterbacks.