Zack Wheeler, No. 45, of the Mets leaves a game...

Zack Wheeler, No. 45, of the Mets leaves a game against the Washington Nationals during the sixth inning at Citi Field on April 7, in Queens. Credit: Jim McIsaac

As the walks piled up for Zack Wheeler, and the Citi Field crowd cheered sarcastically for a long overdue strike, the Mets had to be consumed with a single prevailing thought: Weren’t we supposed to be done with this?

Just as kids get chicken pox only once, Wheeler was assumed to have built up an immunity to this degree of wildness. But seven walks in 4 2/3 innings? Throwing more balls (52) than strikes in 103 pitches? That’s a sickness the Mets believed they had cured with Wheeler, only to see a recurrence of the symptoms Sunday afternoon. 

Don’t let the final score fool you. The Mets’ 12-9 loss to the Nats wasn’t really that close, and Wheeler, more than anyone, was the reason. He laid the foundation by digging a 7-1 hole that deepened to 12-1 before the Nats’ porous bullpen did what they do.

During the second inning, Wheeler allowed six of seven Nats to reach, a five-run rally punctuated by Howie Kendrick’s sacrifice fly. In the fifth, Wheeler issued four walks, forcing in a run, and let another score on a wild pitch. The boos escalated to the loudest heard at Citi in this very young season, and Wheeler knew every decibel was deserved.

“It was an embarrassing day for me,” he said.

The seven walks were the most by a Met since Oliver Perez in 2010, and for those who remember being eternally frustrated by the enigmatic lefty, that’s not a name you want to be associated with. Perez was always hyped for his high-ceiling potential, yet could never consistently harness a lightning-bolt arm during his Flushing tenure.

Wheeler was troubled by similar command issues early in his Mets career -- further compounded by the time missed time due to injuries -- but he appeared to turn the corner last season. He entered Sunday on a 9-1 surge with a 2.03 ERA in his last 12 starts dating to July 24, and had pitched at least seven innings in 10 of those dozen, with nine quality starts.

Finally, with free agency only a season away, Wheeler had become the front-end starter everyone imagined him to be. The glitches were fixed. And if there was a hiccup, Wheeler had shown the ability to self-correct on the fly, minimizing damage on the rare occasion he slipped.

What happened Sunday was only one start, and Mickey Callaway, along with pitching coach Dave Eiland, was quick to diagnose the problem. But rebooting Wheeler in the days leading up to his next start is small consolation after dropping two of three to the Nats. Apparently, Wheeler was off mechanically -- “His arm was a little late,” Callaway said -- and that messed irreparably with his command.

Although Wheeler admitted to not being much of a “video guy,” he ducked into the control room between innings to check his delivery. That helped straighten him out enough to retire seven in a row before coming apart again in the meltdown fifth.

“It was a little surprising,” Callaway said. “I was kind of concerned, like, OK, what’s going on here? The more and more we paid attention, you could tell his arm was late. The good thing is we fixed it before -- and this is one time, two innings worth of it -- we’ll be able to fix it again.”

Which is fine, if the Mets were dealing with a work-in-progress Wheeler. But he’s meant to be a finished product this season, not prone to these midgame blow-ups, and his ERA after two starts is 10.24. This particular malfunction is nothing new -- Wheeler said he just got much better with the maintenance of it last season. Why he couldn’t just do the same thing Sunday is the confounding part of this.

“It’s a pretty simple fix,” Wheeler said.

And there’s no reason to believe Wheeler can’t correct it for next time. But the Mets’ rotation, widely regarded as one of the best in baseball, is saddled with bigger expectations. Wheeler is counted on to be a special No. 3, not just filler for the back end, and he allowed more than four runs for the first time since the half-dozen he gave up June 12 in Atlanta.

“He just couldn’t throw the ball over the plate,” Callaway said. “Chalk it up to a bad day. I think it has to happen consistently for you to start worrying about it.”

If Wheeler suffers that severe of a relapse, the Mets better hope Dallas Keuchel is still available.

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