For the Seahawks, this has been a season of great accomplishment built on a foundation of great fragility.

So many improbably close wins, so little margin of error. It’s not fair to call it smoke and mirrors, but there has been a distinct element of sleight of hand. Ten of their 11 victories are by a one-possession margin, two of them in overtime, with an undeniable litany of favorable breaks along the way.

(Rich Boudet / The Seattle Times)

And now, in the wake of a demoralizing 27-13 defeat to what had been a subpar Arizona team — an outcome that was actually the least of their worries on a soul-crushing Sunday — it is proper to wonder:

Is their joy ride chugging to a halt?

As they head into their most important game of the season, a showdown with the San Francisco 49ers for the NFC West title, the Seahawks are a broken team.

They are broken physically, having received the devastating news that, on top of all the other injuries, running back Chris Carson is out for the season after suffering a hip injury. So is his backup, C.J. Prosise, and so already was emerging second-year back Rashaad Penny.

Offensive-line anchor Duane Brown will be undergoing surgery. The defense is sprinkled with key players fighting desperately to get back on the field. Many didn’t make it on Sunday, including Jadeveon Clowney, Shaquill Griffin and Quandre Diggs, three stalwarts.

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That was certainly a factor in the concurrent reality their execution and production was broken on Sunday, too. After a nearly flawless drive on their first possession, the Seahawks sputtered and faltered on offense the rest of the way.

Russell Wilson struggled to get a rhythm going behind a makeshift offensive line (“stagnant” was the word he used to describe their attack), with the running game reduced to rookie Travis Homer. And the defense, after an initial three-and-out start, was gashed for an 80-yard touchdown run by Kenyan Drake that turned the game. At key junctures of the second half, the Seahawks were unable to get the Cardinals off the field, even when quarterback Kyler Murray left with an injury.

Wilson, harassed all day by the Cardinals pass rush and battered in particular by the extraordinary Chandler Jones, knows perceptions can turn on a dime in the NFL. And he knows  the Seahawks’ bandwagon is about to thin out — even if they bring in Marshawn Lynch to boost the running-back corps and shake up the room.

“Before this game, everybody was talking about how we were one of the best teams in the NFC,’’ Wilson said. “Now things are probably going to change.”

The key question, of course, is if Seattle’s spirit has been broken as well. That would be out of character for a Seahawks team that has shown a propensity over the years for bouncing back from tough defeats under Pete Carroll. Linebacker Bobby Wagner reminded everyone of what happened in 2013 in the next-to-last week of the season — also against Arizona at home, a 17-10 loss.

“Me, K.J. (Wright) and Russ, we’ve been in a lot of situations, good and bad, at the end of the season,’’ Wagner said. “In 2013, there was a similar situation and it turned out really well for us. We lost to Arizona right before the end of the season and we won the Super Bowl.”

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Of course, that team was teeming with young superstars that had been steamrolling most opponents, not eking out wins. The degree of difficulty is greater now, especially with such a depleted roster. All eyes now turn toward general manager John Schneider to see how he and Carroll will address their dire situation at running back.

“There’s so much to figure out,’’ Wilson said in the wake of the defeat. “ … I don’t think there’s anybody better than us to be able to figure out how to answer back.”

Throughout the locker room after the game, players vowed to be ready for the 49ers. But the loss put them in a much more precarious situation with regard to seeding. Rather than being assured of at least a No. 2 seed and a first-round bye with a win on Sunday, now they can beat the 49ers and still be the No. 3 seed, requiring them to play in the first round. And there are scenarios where a loss could drop them all the way to No. 6.

The lower the seed, of course, the more the Seahawks stand to be on the road in the playoffs. Their three Super Bowl appearances have come in years where they had home-field advantage throughout. Of course, it’s fair to wonder if the vaunted CenturyLink edge is waning slightly. The Seahawks are 4-3 at home this season (compared with 7-1 on the road) and have absorbed nine home defeats in the last three years.

Those are just numbers, however. The bigger worry is what everyone’s eyes saw on the field Sunday at CenturyLink. And the players they didn’t see.

“Boy, nothing worked out the way we wanted it to,’’ Carroll said. “There were so many things that weren’t right for us today.”

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Can they fix it by Sunday? Veteran Bradley McDougald saw an opportunity amid all the injuries.

“That’s when you show who a true team is,” he said. “That’s how you can tell a true championship team.”

The Seahawks still have those aspirations, but Sunday’s performance — and aftermath — showed just how daunting that path will be.