ENGLEWOOD, Colo. -- Quarterback Case Keenum would like to leave the Denver Broncos' power brokers with the best possible last impression he can muster.

And there's just one more afternoon's worth of football left for that as his Broncos will miss the playoffs for the third straight time since winning Super Bowl 50. The Broncos (6-9) figure to go into the fourth consecutive offseason since Peyton Manning retired with at least some questions about both their short- and long-range plans at quarterback.

Keenum, who turns 31 in February, signed a two-year, $36 million deal last March, a prove-it sort of contract that the quarterback hopes is just the start of a long run in Denver. And Sunday's season finale against the Los Angeles Chargers is his last chance to show the Broncos what he can do before roster decisions are made this offseason.

"I don't look at it that way," Keenum said after Wednesday's practice. "Yeah, I want to play here the rest of my career. I look at it as I have to do my absolute best every week, it's not just this week. I'm not just going to turn it on. I've done the best that I possibly can every week, played as hard as I possibly can. Have I done my best? In my own mind, I could have done better, I should have. You could say ‘coulda, shoulda, woulda.' I've learned from my mistakes and am going to continue to grind. That's who I am. We'll talk about all that at the end of the year."

After rotating three different starters in 2017 -- twice -- with decidedly mixed results, finding a solution at quarterback was the Broncos' top offseason priority after they finished 5-11. After an extensive review of the quarterbacks available in both free agency -- including some early interest in Kirk Cousins -- and the draft, the Broncos chose Keenum.

General manager John Elway went as far as to say last March, when Keenum was formally introduced, that Keenum had a better season in '17 than Cousins did. The Broncos did not use a draft pick on a quarterback last April.

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But Denver's passing game hasn't been anywhere close to consistent. Not with three starters in the offensive line on injured reserve (the Broncos essentially have played four tackles up front, to go with a guard who moved to center), two tight ends who started games in 2018 now on injured reserve, Elway's trade of wide receiver Demaryius Thomas and wide receiver Emmanuel Sanders' season-ending Achilles tendon injury.

The result has been an offense not too different from last season. Trevor Siemian, Paxton Lynch and Brock Osweiler combined for 208.3 passing yards per game over the course of the 2017 season, which ranked 20th in the league. Right now, the Broncos, with Keenum having played 994 of 995 snaps on offense, are ranked 19th in passing yards at 227.1 per game.

In scoring, the Broncos finished the disappointing 2017 season 26th in the league at 18.1 points per game; they are just slightly better this season at 21.3, ranked 22nd.

"Early in the year, there may have been some red zone opportunities that we missed," Keenum said. "Then just not moving the ball in the first half. It's a lot of different things. You just try to keep growing and try to keep scoring. Try to keep creating explosive plays, scoring opportunities. There's a lot of things ... this week we've got to score points. This is a very talented offense and we've got to stay on the field. Put together some drives. ... We need to put some more points on the board."

Keenum's 14 interceptions are tied for third-most in the league. Two of them came during Monday night's loss to the Oakland Raiders, when the Broncos were in catch-up mode in the second half after trailing 17-0 at intermission.

Broncos coach Vance Joseph said Keenum was "playing his best football" during a five-game stretch as October turned to November. Keenum did not throw an interception and the Broncos went 3-2 in those games to move to 6-6 before the current three-game losing streak. The Broncos have not won or scored more than 16 points since Sanders' injury.

Keenum said Sunday's game would allow him to put a quality effort on his résumé heading into offseason work.

"Nobody in this building likes losing, nobody in this city likes losing, I've found -- it's a fact," Keenum said. "Nobody more than me, I hate it. To go out on a high note, to beat the team going to playoffs, maybe show some other teams how to beat them. We've got a great opportunity here, a great opponent and it would be a great way to end the year."