To many NFL observers, Brandon Beane and Sean McDermott, the Bills’ general manager and head coach, respectively, had made an egregious mistake.

That’s what happens when a team errs in selecting a quarterback in the draft’s first round … especially when trading up to do it.

When Buffalo chose Wyoming’s Josh Allen with the seventh overall pick in the 2018 lottery, after moving up five spots via a trade with Tampa Bay, the eye rolls were almost immediate.

Five quarterbacks were taken in that opening round, the other four from Power 5 conferences: No. 1 Baker Mayfield (Oklahoma), No. 3. Sam Darnold (USC), No. 10. Josh Rosen (UCLA) and No. 32. Lamar Jackson (Louisville).

And when Allen struggled with accuracy, decision-making and fumbles his first two years, it appeared the criticism and cynicism were justified.

Then came Season 3.

SUDDENLY, Allen has become the franchise QB Beane and McDermott envisioned … and that’s not comparing him to Ryan Fitzpatrick and Tyrod Taylor, we’re talking Jim Kelly and Drew Bledsoe.

That’s the level — or better — at which he has performed so far this year.

Looking at that 2018 first-round QB class, Darnold (Jets) and Rosen (now with the Bucs after failed stints with Arizona and Miami) aren’t even in the conversation.

Jackson, taken with the round’s final pick, became a sensation last season when he produced 43 touchdowns (36 passing, 7 rushing in 15 games) but has been pedestrian this year due a combination of injury and opposing teams learning how to defend him.

Mayfield (6-foot-1, 215 pounds) has emerged, leading Cleveland to a 9-3 start — the same as Buffalo — and became the leader the Browns expected. But Allen has his own leadership skills — albeit not quite as passionate — plus a way bigger arm and more impressive rushing proficiency based on his size (6-5, 237) and speed.

What’s certain is, the Bills wouldn’t trade him for any of the other four.

AND HE emphatically made that case in Monday night’s impressive neutral-field, 34-24 win over the 49ers at Arizona’s State Farm Stadium.

His numbers were glittering: 32-of-40 passing for 375 yards, four touchdowns and no interceptions. He became the first Buffalo QB to attempt at least 40 throws and complete 80 percent of them.

Allen also didn’t come close to making a bad decision. Afterward, as usual, he was quick to credit his teammates and, from Day 1, he’s taken full responsibility for bad plays, a lesson it took Kelly a bit longer to learn.

The performance against San Francisco marked his sixth 300-yard passing game — one behind Bledsoe in a single season (2002) — and in three of those he’s thrown four TD passes, that combination a franchise record.

And, it’s worth noting, Allen hasn’t fattened his yardage totals late in games where Buffalo was losing and had to pass. The Bills have won all six of his 300-yard efforts in which he’s totaled 17 touchdowns.

In a dozen starts this season, he’s produced 33 touchdowns (26 passing, 6 rushing, 1 receiving), tied for second in the NFL with Seattle’s Russell Wilson and Kansas City’s Patrick Mahomes, behind only Green Bay’s Aaron Rodgers (37).

For the record, Buffalo’s franchise mark is 34, set by Kelly in 1991, leaving Allen four more games to pass him.

From a league standpoint, Allen is the first quarterback in NFL history to have two 400-yard games (417 versus Miami, 415 against Seattle) with four touchdown passes in each.

In the current league standings, he’s fifth in passing yardage (3,403, but only 73 out of third), tied for sixth in touchdown passes and sixth in passer rating (105.9).

BUT THE most important result of Allen’s performance — Buffalo’s first Monday night win in 21 years — has little to do with statistics.

In the Bills’ two previous nationally-televised games this season, they were manhandled at Tennessee, 42-16, and lost at home to defending Super Bowl champion Kansas City, 26-17.

In those two games, his combined numbers were 59% completions for an average of 193 yards with four TD passes, three interceptions and a passer rating of 75.5.

However, against the Niners, Allen demonstrated for a nationwide audience that he belongs among the NFL’s elite quarterbacks.

If the playoffs began today, Buffalo would be the No. 3 seed, behind Pittsburgh (11-1 with a bye) and Kansas City (11-1), and would host division-rival Miami at Bills Stadium a week after entertaining the Dolphins at that same site in the regular-season finale.

But how great would it be if, in the season’s final quarter, that first-round playoff became Cleveland versus Buffalo, Mayfield against Allen?

(Chuck Pollock, a Times Herald senior sports columnist, can be reached at cpollock@oleantimesherald.com).