Eli Manning and the Giants had every reason to be optimistic. Even until very recently.

“I thought we would have an opportunity this year, and the way the season was ending up at the halfway point, we had a great opportunity,” the quarterback said this past week, reflecting on what quickly deteriorated into a third straight losing season and a fourth straight fruitless postseason push.

“I felt good about this season and the second year in this offense and some of the guys we had and the playmakers,” he added. “[It] just didn’t work out for us. We didn’t make some critical plays in critical moments of the game this season.”

InteractiveGiants 2016: Keep 'em or dump 'em?

In a season defined by 21 total points — that’s the combined difference in seven of the team’s nine losses, none of them by more than six — it stands to reason that there would be a handful of moments that stand out as wasted opportunities. A win in any of those games would have altered just about everything for which 2015 will be remembered.

The season of heartache began in Dallas and continued right up through the Week 14 game against the Panthers. “Even the last couple of weeks, we haven’t done enough to make the playoffs,” Manning said. “We just couldn’t win some close games, and we had a lot of them.”

Here are the five most damaging moments of 2015, the plays that scuttled the season. Some of them are seared in fans’ memories; others may require a bit of a reminder regarding the exact circumstances. But all of them changed the tone of the year and ultimately could affect the direction of the franchise.

advertisement | advertise on newsday

The Patriots drop

All he had to do was catch the ball. It was, perhaps, the worst pass Tom Brady threw all season, and maybe the worst he’s thrown in a decade. A wobbly floater down the middle of the field with no Patriots teammates around it. Dominique Rodgers-Cromartie seemed poised to field it like a punt for the Giants. But rookie safety Landon Collins inexplicably jumped in front of him, tried to hold on to the ball as he hit the turf hard thanks to his awkward leap — and dropped it.

Giants videos

That gave the Patriots another chance to drive for the go-ahead field goal, which they converted with one second remaining to beat the Giants, 27-26.

The third-and-5

Three days after the Cowboys and Eagles both lost on Thanksgiving Day, the Giants had a chance to take a firm grip on the division lead. Instead they “slept-walked,” as Tom Coughlin put it, through the first three quarters of the game and fell behind Washington 20-0. Still, they woke up in time to score two fourth-quarter touchdowns — the second on a sick one-handed catch in the end zone by Odell Beckham Jr. — and the suddenly wide-awake offense seemed poised to punch in the third to take the lead. The only thing they lacked was the football.

The defense could not get that for them. Washington converted a critical third-and-5 with 3:29 remaining on a 20-yard pass to Jordan Reed with Craig Dahl in coverage. The Giants did not get the ball back on a punt until there were 19 seconds remaining.

advertisement | advertise on newsday

The Dallas debacle

In a game that seemed to set the tone for the entire season, the Giants blew a 10-point lead with 8:01 left in the game by allowing the Cowboys to score a pair of touchdowns on drives that covered a combined 148 yards on 12 plays and took just 4:20.

But it wasn’t the Dallas touchdowns that became the talking point for the game. Manning lost track of the Cowboys’ timeouts because one was given back to them after a penalty, and he mistakenly told running back Rashad Jennings to not score a late touchdown that would have given the Giants a 30-20 lead with less than two minutes remaining. On first-and-goal from the 4, Jennings ran twice and gained three yards. Then, on third-and-goal, Manning had another brain freeze when he rolled to his right. Instead of taking a sack that would have kept the game clock rolling to under a minute, he threw an incomplete pass. The Giants settled for a field goal and Tony Romo had 1:29 left to score the game-winning touchdown. He needed just 1:22.

advertisement | advertise on newsday

The Jets decision

This was the moment when Tom Coughlin officially lost faith in his defense, and it was the offense that burned him. He believed the Giants would not be able to hold a potential 23-10 lead in the final eight minutes, so rather than attempt a gimme field goal on fourth-and-2 from the Jets’ 4, he decided to try for a touchdown that would give him some extra cushioning and a three-score advantage.

He got neither.

Eli Manning’s pass for Rueben Randle was intercepted in the end zone by Rontez Miles with 8:42 remaining. The score remained 20-10, and the Jets needed only 10 points to tie before winning in overtime.

The Odell drop

With no more wiggle room in the standings, the Giants weren’t looking to simply make a statement by beating the undefeated Panthers. They needed a win. And it seemed as if they would be off to a good start when Manning threw a deep pass down the middle of the field for Beckham on the opening drive.

Beckham was several yards behind cornerback Josh Norman, and it looked like an easy touchdown as the ball settled down toward the Pro Bowl receiver.

But he dropped it. The best playmaker in the NFL dropped it.

The game ended in another almost inconceivably late loss for the Giants, the third of the season in which the deciding points were scored with one second or less on the clock. But the drop by Beckham hovered over everything that transpired. The deciding play of the game seemed as if it came early in the first quarter, not at the end of the fourth.