John Mara decided there was no point in delaying the inevitable.

With enough damage having been done to the Giants’ brand during a 2-10 plummet punctuated by the pathetic mishandling of iconic quarterback Eli Manning’s situation last week, the co-owner ripped off the bandage instead of waiting until after the season, as he had promised. Really, there was no other choice.

A day after Manning’s streak ended at 210 starts, a day after the Giants were embarrassed further in one of the most disappointing seasons in franchise history, Mara fired coach Ben McAdoo after 29 games on the job and parted ways with general manager Jerry Reese, the architect of an underachieving team headed for a last-place finish.

There was no point in waiting. Not with fans ready to bring their figurative pitchforks to Sunday’s game against the Cowboys to express their rage at a coach who was in over his head.

McAdoo had just sullied the reputation of one of the team’s greatest players by benching Manning and replacing him with — of all people — Geno Smith.

McAdoo somehow thought Smith could be something different from what he’d been in his four seasons with the Jets — a turnover-prone quarterback with an immature streak. He wasn’t. Smith lost two fumbles in a 24-17 loss to the Raiders and then offered an unsolicited rip job of his former Jets coach, Rex Ryan. Smith later apologized on Twitter — a sequence of events all too familiar for Jets fans who had grown tired of his act.

Mara said Manning’s situation had nothing to do with the timing of Big Blue’s Black Monday. Nonsense. With a fallout so vicious that even Mara said last week that it had caught him off guard, the cause-and-effect here is obvious.

Mara has seen things get this bad around here. He remembers fans burning their season tickets late in the 1978 season. He was at Giants Stadium the afternoon of Dec. 15, 1978, when a single-engine plane flew over Giants Stadium carrying the banner, “15 Years of Lousy Football — We’ve Had Enough!”

You can only imagine what the scene would have been like Sunday at MetLife Stadium with McAdoo as the coach and Smith as the quarterback. Mara imagined it, too, and wisely made a move to avoid the hysteria that surely would have unfolded.

There was a hint of what might have happened during warm-ups for Sunday’s game. As Manning took the field, about 25 fans wearing No. 10 Giants jerseys gathered in the corner of the end zone and chanted “Eli Manning! Eli Manning!”

There would have been thousands more like them at MetLife — perhaps even former Giants who appeared ready to wear Manning jerseys and stand on the sideline in support of the spurned quarterback.

“If you want to blame anyone on that, blame me,” Mara said Monday about how the Manning controversy unfolded. “I could have overruled it.”

He should have. He either should have ordered McAdoo to reinstate Manning as the starter or should have fired McAdoo right then and there. Now an ironman streak dating to 2004 is over, and all because of this absurd plan to get a look at Smith and eventually Davis Webb.

Manning has become an incredibly sympathetic figure as a result of the botched plans, and his popularity has soared. He said after Sunday’s game that he wants to play in 2018, but it’s anyone’s guess whether it will be with the Giants. Blame McAdoo for that, but blame Mara, too, because he had his chance to make it right last week and didn’t.

It’s now on Mara to get his next two hires right and get his franchise back on track after an incredibly swift fall from grace. With former Giants general manager Ernie Accorsi, who set the stage for their Super Bowl victories after the 2007 and 2011 seasons, serving as a consultant, they must get a quality personnel executive and then a high-caliber coach.

Mara can only hope that his team will find its way out of the smoldering ashes as successfully as it did after the last time it made simultaneous hires for GM and coach. George Young’s arrival as GM in 1979 and his hiring of coach Ray Perkins and later Bill Parcells transformed the Giants from a laughingstock into a Super Bowl champion.

The Giants are at the bottom again, and the decisions Mara makes in the coming weeks ultimately will define his team.

It’s now on him.

All of it.