CLEVELAND — Joe Staley arrived at work Sunday and, within a few hours, discovered he had received the wrong memo.

“I thought we were going to show up and play,” said the 49ers offensive tackle.

Instead, the 49ers showed up here and displayed … well, whatever you want to call that pile of foul mulch they dumped on the turf of FirstEnergy Stadium.

The 49ers were not an NFL team that was professionally prepared to beat another NFL team. The 24-10 loss to Cleveland was not something that any 49ers player or coach chose to defend.

“I think we all took a step backward today,” coach Jim Tomsula said. “We played poorly today. There isn’t a guy in the locker room that doesn’t own some part of this, starting with me.”

All right, let’s start with him.

The fingerprints of such a woeful defeat were indeed numerous. But the practical matter is that the 49ers roster, while greatly flawed and gap-ridden, certainly contained enough talent to defeat a Browns team that owned a pathetic 2-10 record before Sunday’s kickoff.

“Maybe we just came out a little flat,” said 49ers linebacker Ahmad Brooks. “That’s no excuse. Maybe we got a little bigheaded and just thought a victory was going to happen.”

Bigheaded? How on earth could the 49ers be bigheaded, given their own modest total of just four victories?

Yet that is what we witnessed Sunday. The 49ers’ effort for much of the afternoon was at Pro Bowl level — and not the good kind. They played with the scrimmage-like non-intensity frequently seen in the NFL’s semi-serious all-star game.

Tomsula deserves the most blame for that. His job, at minimum, is to have his team ready to beat opponents it should beat. The 49ers were coming off an overtime victory against Chicago a week ago that should have created confidence and momentum. But somehow, Tomsula allowed his players to twist that into overconfidence and smugness.

Time to be blunt. If Tomsula did not have his team prepared to win this game, it raises serious questions about whether he can have any team prepared to win any game in the future. His status for next season, before Sunday, appeared to be sort of safe because the team appeared to be making progress over the past month. Scratch that.

Also significant were the postgame comments of Cleveland coach Mike Pettine. Someone asked him why the Browns’ rushing game (230 yards) was so successful against the 49ers.

“We felt good about the run plan and the matchup,” Pettine said. “There were some things schematically we thought we could take advantage of, especially in some of the spread run game. … We recognized a weakness and exploited it.”

It is extremely rare to hear an NFL head coach speak about exploiting a schematic advantage over an opponent — because basically, you are bragging that you out-coached the other guy.

So it wasn’t just that Tomsula and his staff didn’t have the 49ers mentally geared up to beat the Browns. The X’s and O’s were also defective.

But you didn’t need to tell that to 49ers quarterback Blaine Gabbert. He was sacked nine times while trying to execute the game plan of offensive coordinator Geep Chryst. To be sure, Gabbert should have thrown away the ball a few times to avoid some of those sacks. And the 49ers offensive line is shaky.

But the sacks also happened because Chryst’s playbook was hardly effective. Consider: Barring a garbage-time touchdown drive in the game’s final four minutes, the 49ers offense produced 127 net yards and one field goal.

If Chryst can’t figure out a way for the 49ers offense to score more than one touchdown in garbage time against an opponent that had been allowing almost 30 points per game, it raises serious questions about whether he should continue in his job.

And if 49ers defensive coordinator Eric Mangini could not align his men to stifle skittery second-year quarterback Johnny Manziel or a Browns’ rushing attack that was averaging just 74 yards per game … then you might as well call Mangini’s status into question, too, despite his fairly good work this season.

Significantly, all of this occurred under the gaze of the entire York ownership family — Jed, Denise, John, Tony, Jenna and Mara. They were all in attendance after either motoring up from their year-round home in nearby Youngstown or flew in from California. The 49ers’ performance could not have produced much laughter or contentment in the visiting owners’ suite.

Will that yield drastic action after the season? Ownership and management have been sending out a vibe that the victory at Chicago proves the team is heading in the right direction. That is now officially wishful thinking.

There are three games left in the season, three more games for Tomsula to rally and build his case that he has things pointed in the right direction. He said Sunday that he still believes the team is improving and that the “poor” performance was an “execution problem” and not an “effort problem.”

Staley, when asked if the 49ers’ problems were execution-related or structure-related, said: “I think it’s both.”

I think Staley is right. When the 49ers management parted ways with former coach Jim Harbaugh last winter and introduced the current staff, the spin was that the coaches were “teachers” and that it’s exactly what the roster needed.

What did Tomsula and his coaches teach the team Sunday?

Read Mark Purdy’s blog at blogs.mercurynews.com/purdy. Contact him at mpurdy@mercurynews.com. Follow him on Twitter at twitter.com/MercPurdy.