PITTSBURGH — Mike Tomlin laughed. Then he bit his tongue.

Asked if he could describe a bafflingly flat 24-10 loss to Arizona on Sunday in one word, the longtime Pittsburgh Steelers coach smiled, let out a somewhat sarcastic chuckle, and cautioned that he needed to watch what he said before settling on “subpar.”

That’s one word for it.

Here’s another. Well actually, here are two: poorly timed.

The NFL regular season is a grind both physically and mentally, particularly for a team such as the Steelers that engages in rock fights weekly. Upsets happen every Sunday (or Monday, or Thursday). No team — no matter how good — is immune.

Flat spots happen. They are unavoidable. It’s one of the reasons the 1972 Miami Dolphins pop champagne every year when the last unbeaten team falls.

Yet the Steelers had thought they’d gotten their mystifying no-show out of the way in Houston in Week 4, a loss that looking back doesn’t seem nearly as bad now as it did in the moment given the Texans’ quick rise to contention.

It turned out to be merely a prelude for four quarters of largely inept play against a team that walked onto the Acrisure Stadium turf 8-28 since a 10-2 start to the 2021 season.

Penalties. Missed tackles. Missed opportunities. The Steelers — who have thrived in tight games all season and hadn’t lost to a team that entered the game with a losing record since Week 4 of the 2022 season — put on a clinic on how to lose.

They also provided a reminder that they are not talented enough, by a long shot, to overlook anyone. A user-friendly part of the schedule seemingly designed to bolster their postseason chances instead now looks like a minefield, one they will have to navigate in the short term with Mitch Trubisky taking over at quarterback while Kenny Pickett recovers from right ankle surgery.

While star outside linebacker T.J. Watt allowed the Steelers got their “(butts) kicked,” he also made it a point to say they were prepared to play.

If so, they had an odd way of showing it. Sure, the offense looked as underwhelming as ever a week after a “breakout” (by Pittsburgh’s diminished standards) performance in a victory over Cincinnati.

Yet the offense didn’t let Arizona go 99 yards in 15 plays at the end of the first half. And unlike the 2008 Super Bowl, this time there was no 100-yard interception return by James Harrison to bail them out. The Cardinals had one touchdown pass overturned on replay then proceeded to score the following play anyway.

Pittsburgh is only in the playoff race thanks to the defense. Yet on a day in which the Steelers could have created a little breathing room over the teams chasing them for a postseason berth while simultaneously putting at least a little heat on AFC North-leading Baltimore, the defense looked ordinary.

For a team almost pathologically averse to scoring, the defense can’t afford a quarter off, let alone four of them.

The silver lining is that Cleveland — now on its fourth quarterback — also lost. So did Denver. An increasingly pivotal game against resilient Indianapolis looms in two weeks.

Ten wins probably gets Pittsburgh into the playoffs, warts and all. Beating a rebuilding team that came in 31st in the league in yards allowed would have nudged the Steelers closer to that number.

Instead, for long stretches during a rare December thunderstorm, it was hard to tell which team was a legitimate postseason contender and which was already looking to 2024.

And that is no laughing matter.

WHAT’S WORKING

It feels as if you can cut and paste “the running back tandem of Najee Harris and Jaylen Warren” into this space every week. The duo combined for 122 yards rushing against the Cardinals and averaged nearly 6.0 yards per carry.

WHAT NEEDS HELP

The offensive line remains an issue, particularly in pass protection. Center Mason Cole has struggled with providing consistent shotgun snaps (two low ones on Sunday led to a sack and a fumble) and the Cardinals were able to pressure Pickett and Trubisky frequently, leading to rushed throws or — in Pickett’s case — injury.

KEY NUMBER

2-3 — Mitch Trubisky’s record as a starter in Pittsburgh.