ENGLEWOOD, Colo. -- By the time the last play of the dismal 2018 season had been run by the Denver Broncos, they had lost 10 games and chewed up and spit out the fourth starting quarterback in a two-year span, Case Keenum.

The Broncos' 21 losses in two seasons put them in a place they had not been in decades, and they were no closer to finding a replacement for Peyton Manning than they were the day after he retired in March 2016.

None of the five quarterbacks the Broncos had drafted in general manager John Elway's tenure, led by Paxton Lynch in the first round of 2016, were on the roster and Keenum wasn't up to the task. The Broncos fired coach Vance Joseph, and Elway, who oversees football operations, was still staring at the largest hole on his depth chart.

"Yeah, we've shaken the tree, all of the trees," Elway said earlier this summer.

Now, the Broncos hope Joe Flacco can fix all of that. They crunched the numbers, rolled the video and considered all available quarterbacks. They decided Flacco, 34, can right the wrongs.

"I do think I've got a lot left in my tank," Flacco said. " ... I do feel like there is a lot more I can show, no question."

Why Flacco? Why now?

The Broncos want the playbook offensive coordinator Rich Scangarello is installing: an updated version of the West Coast offense. It's the same type of scheme that earned the Broncos the three Super Bowl trophies that reside in the lobby of their suburban Denver complex, and it's one that Flacco can run.

"It's a fit for me, there's no doubt. There's a familiarity there. I've been around success in this offense. There's a lot to like in all of that," Flacco said. " ... And I'm as healthy as I can be, and I'm looking at playing as long as I can."

One of the first items on coach Vic Fangio's to-do list was a review of potential replacements for Keenum. Before leaving for the Minnesota Vikings, Gary Kubiak offered his endorsement of Flacco -- Flacco had his best all-around season with Kubiak as the Ravens' offensive coordinator in 2014 -- but Fangio conducted his own analysis. He poured through a pile of game video of potential replacements and asked Scangarello to do the same.

Fangio made sure the two did it independently, and when each had finished, they both had graded Flacco as the best potential option.

But the best quarterbacks in their primes simply don't hit the open market. Those who do, or are dangled in trade, are there for a reason, whether it be age, injury or their level of play. Arguably, even the most decorated player ever to hit free agency -- Peyton Manning -- did so because of significant medical questions.

After missing his final season with the Indianapolis Colts (2011) in the wake of his fourth neck surgery, Manning couldn't complete a full throwing workout at Duke University when Broncos officials traveled there to gauge his recovery. But Elway rolled the dice, and the greatest four-year stretch in the team's history -- two Super Bowl trips, one Super Bowl win, four division titles and the league's single-season scoring record -- followed.

The Broncos have rolled the dice again on Flacco, a veteran quarterback who carries his own set of questions when it comes to age and injuries. But after watching the churn of the team's quarterback prospects, Elway turned to experience. After Manning retired, the Broncos tried going young behind center, and Trevor Siemien led the team to a 9-7 finish in Kubiak's last season as head coach in 2016.

But 2017 was a mess. Siemian, Lynch and Brock Osweiler started games and were benched during the 5-11 season. Last season, Keenum, coming off of an 11-3 season as a starter for the Minnesota Vikings, was Elway's choice, because of his familiarity with the guts of the Shanahan/Kubiak scheme.

It went so poorly Elway was already on the road in October to see Oregon's Justin Herbert play in case he entered the April draft. As the season limped to a close, the Broncos never gave much consideration to keeping Keenum after they discovered that Flacco could be available. They traded Keenum to the Redskins shortly after finalizing the deal with the Ravens for Flacco.

The Broncos agreed to pay Keenum $3.5 million of his salary guarantee and a $500,000 restructure bonus to tweak his contract so the trade could be made.

"We looked at it: the success we've had in this system, the success Joe's had in this system with Gary [the Ravens' offensive coordinator in 2014], the tools Joe has to make all throws," Elway said. "And that experience, that experience is something that gives the team confidence ... the feeling that can give the guys around the quarterback is something we need."

Flacco's age and experience were on the pro side of the Broncos' ledger, not the con. Elway has gone as far as to publicly say that Flacco is "in his prime."

Although Flacco has missed games in just two of his seasons, he has dealt with knee, back and hip injuries in recent years, a fact that pushed the Ravens to keep Lamar Jackson in the lineup even after Flacco was cleared to return from a hip injury last season.

Elway, Fangio and Scangarello have all said Flacco has the arm to push the ball down the field, but that might be the biggest question of all, one that can't be answered until Flacco is standing in against defenses with full game plans in place. He flashed deep ball completion after deep ball completion in drills for the past week, as well as on a 45-yard toss to Emmanuel Sanders up the left sideline Monday night against the 49ers that was called back by a holding penalty, and his teammates like what they've seen so far.

"Flacco's a baller" is how Sanders put it. " ... I said that. Look at him throw. He can put it out there, absolutely."

Last season, in his seven starts, Flacco had four completions of more than 33 yards, and in his most recent full season, in 2017, he had seven of those completions. He has averaged fewer than seven yards per attempt in four of his past five seasons. Last season, nine quarterbacks averaged more than eight yards per attempt, and three (Patrick Mahomes, Drew Brees and Russell Wilson) were at nine or more yards.

"I've said, when you watch him throw every day, he's got all the throws," Elway said. "He's got touch. He can get the ball downfield. Joe's best years were in the system we're going to run, and I just think he wants to prove a little something with a lot of football left in him. I believe that."

Flacco has said "I throw the ball better" now than as a young passer. Scangarello said, "It's up to us to put everybody, Joe included, in the right spots to move the ball and score some points."

Flacco's teammates believe in the résumé and the cool, calm demeanor. "Super Bowl champion. That's it," as guard Ron Leary put it.

"It's always difficult to fill that position, and we had our difficulties in trying to do that," Elway said. " ... You do what you think is best for the Denver Broncos, and we finally feel pretty good about that position and where we are."