Eli Manning reacts on the sidelines in the closing minutes...

Eli Manning reacts on the sidelines in the closing minutes of a game against the San Diego Chargers. (Dec. 8, 2013) Credit: AP

Fans here waited eight years to boo Eli Manning again, then made up for lost time with a torrent of abuse that started before yesterday's game and lasted throughout the Chargers' 37-14 rout of the Giants.

Some still were at it two hours after it was over. With Manning en route to the airport, Qualcomm Stadium cleanup workers cheered the name of the Chargers' Philip Rivers and taunted Manning in absentia.

And why not, even a decade after Manning dissed San Diego by saying before the 2004 draft that he wanted no part of its NFL franchise.

But Manning also would have been within his rights to remind everyone that between his visits, he won two more Super Bowls than the Chargers have in their history, so it worked out just fine for him.

Here's the thing, though: The embarrassing egg Manning and his friends laid here in front of the fans he scorned, and against the quarterback for whom he was traded, is a conveniently timed opportunity to ask an important question:

Just when will those two Super Bowl trophies (and MVP awards) start to look like ancient history as Manning wraps up his worst full season as a pro, now with 16 touchdown passes and 20 interceptions?

On one hand, the answer is never, because Manning forever will be warmly remembered by Giants fans. But that is the long view. In the short term, Manning will have a lot to prove in 2014 after this debacle.

Does he have another five or so quality years left in him, or have we already seen his best as he approaches his 33rd birthday next month?

Naturally, when I asked if his confidence is shaken, Eli wasn't biting, saying "It's been tough" and "I haven't analyzed the whole season" and "After the season, we'll look at it and try to figure that part out."

Teammates have stuck by him. "We won't lose faith in the fact we have a potent offense led by one of the best quarterbacks in this league," Justin Tuck said. "It's been a struggle a little bit for him this year, but I know he won't ever stop fighting."

Whether this is a trend or a glitch will not begin to be answered until September at the earliest. For now, all we have to go on is what we have seen, and it's not pretty.

Manning was far from the only problem Sunday, but his struggles were by far the most entertaining element for Chargers fans, who booed him mercilessly all afternoon.

That included at halftime, after he completed a Hail Mary 43-yarder to Hakeem Nicks that fell 6 yards short of the end zone -- which sort of defeats the purpose -- and padded his 20-for- 32, 259-yard day, which included one TD pass and two interceptions. (Rivers was 21-for-28 for 249 yards, three TDs, no interceptions and gloating rights, which he refused to exercise.)

Fans resurrected a chant from the Giants' 45-23 loss here in 2005 that meant something similar to "Eli stinks."

The public address announcer goaded them by announcing that Manning's second interception was his 20th this season, and the video board operator flashed an image of a fan holding a blown-up head shot of Manning in a blonde wig, lipstick and earrings. (OK, I'll say it: You stay classy, San Diego!)

After the game, two Chargers staffers posed beside the Manning head shot as Giants security officials Mike Murphy and Vinny Byron, who usually accompany Tom Coughlin off the field, instead guarded Manning.

Did all the abuse bother him? "No, fans have never affected my play,'' he said, "and I kind of go out there and just try to play good football."

None of the above means he won't be his old reliable self next fall. But if it happens, Chargers fans will have to wait to witness it firsthand. His next scheduled chance here won't come until 2021. By then, we'll have a better idea what his 2013 meant.