Neil Best Newsday columnist Neil Best

Neil Best first worked at Newsday in 1982, then returned in 1985. His SportsWatch column debuted in 2005.

If you thought it was uncharacteristic of Eli Manning to make game-turning mental mistakes on not one, not two, but three consecutive plays Sunday night, you should have seen him at his locker afterward.

As he put on his suit in preparation for facing journalists, Easy E looked as angry as he ever gets, at one point cursing under his breath and then shaking his head for a good 15 seconds.

It turned out the Giants quarterback mostly was angry at himself, for reasons that initially seemed straightforward and then got even worse on the day after a punch-to-the-gut, season-opening 27-26 loss to the Cowboys.

Not good, especially given that Manning, newly re-signed for many tens of millions of dollars, is far more important to the near-term future of the franchise than is Tom Coughlin, his partner in poor decision-making Sunday night.

The coach might or might not be here in 2016. Eli will be. And he must be better than he was against Dallas, both in his performance and his thinking, if he would like to continue working with Coughlin beyond their 12th year together.

In fairness, this mostly has been a non-issue to date. As Coughlin said Monday of his quarterback: "It's never happened before. I completely trust Eli, always have. He's extremely into the game."

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Not so much Sunday night. As you saw, heard and read afterward, both Coughlin and Manning accepted blame for an incomplete third-and-goal pass from the 1 that preserved precious time for the Cowboys' game-winning final drive.

"It should have been a run," Coughlin said Monday after having had time to digest it all. "It wasn't."

Nope, it was a play-action pass on which Manning rolled right and -- instead of taking the sack when he saw the play breaking down and keeping the clock moving -- threw the ball out of the end zone, stopping the clock with 1:37 left.

"I have to be smarter in that scenario," Manning said Monday. "That's a bad, bad, bad management of the game."

But Manning had said something after the game that most reporters did not initially understand. He admitted to "bad clock management those final three plays," at which time he thought the Cowboys had one fewer timeout than they actually did.

Hmm. Then running back Rashad Jennings was heard in the locker room talking about being told not to score on first- and second-down runs, an assertion he reiterated to ESPN Monday.

Uh-oh. Initially the Internet lit up with calls for Coughlin to be fired on the spot if he had eschewed what could have been a 10-point lead with less than two minutes left. But it turned out the person who instructed Jennings was none other than Eli Manning, who told him not to score if the Cowboys tried to let him do so, which they had no reason to do given the score, clock and timeout situation.

Unfortunately for the Giants, Jennings listened, unlike Ahmad Bradshaw, who accidentally scored the winning TD in Super Bowl XLVI against Manning's advice.

"It's my mistake," Manning said. "That did not come from the sideline . . . I can't be the one to inform a back."

Coughlin said no such instruction came from the sideline, but Manning said he did tell members of the coaching staff before Jennings' second-down run what he was up to strategically.

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It was around then that he also learned he had miscalculated how many timeouts the Cowboys had because of a strange rule by which the clock does not restart after a penalty on the defense is declined.

The coaches share in the blame for all of the above, but Manning took it all upon himself.

Manning and the Giants can come back from this, certainly, even if it is a strong candidate for the top 10 list of most crushing regular-season losses since the Giants' modern, post-Fumble era began in 1979.

But it was an awful way to start a season for Manning and Coughlin, two guys who, whatever their failings, are expected to know what they are doing as much as any quarterback/coach tandem south of Foxborough.

"To be honest with you, nothing like that has ever happened," Coughlin said of Eli's mental lapse.

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And nothing like it should ever happen again.