ST. LOUIS, MO - APRIL 21: Noah Syndergaard #34 of...

ST. LOUIS, MO - APRIL 21: Noah Syndergaard #34 of the New York Mets delivers a pitch against the St. Louis Cardinals in the second inning at Busch Stadium on April 21, 2019 in St. Louis, Missouri. (Photo by Dilip Vishwanat/Getty Images) Credit: Getty Images/Dilip Vishwanat

ST. LOUIS — Forty-four pitches and five outs into Noah Syndergaard’s afternoon Sunday, pitching coach Dave Eiland made the slow walk to the mound for a chat. Not the first sign that something was going wrong — again — but maybe the most conscientious one.

Eiland’s encouragement helped Syndergaard escape the inning but merely delayed his latest meltdown in the Mets’ 6-4 loss to the Cardinals. He allowed six runs (four earned) in five innings, raising his ERA through five starts to 5.90.

Syndergaard’s poor outing meant four homers from the Mets weren’t enough to salvage a series win. Their best start in this series came from Jason Vargas, who allowed one run in four innings Friday.

The Mets (11-10) finished their 10-game, 11-day road trip against three teams expected to contend for playoff spots at 4-6. They split the first series and dropped the other two. And going home doesn’t mean a break, either. They will begin a three-game series against the Phillies on Monday night.

“It would’ve been a great win today, but I let the team down,” Syndergaard said. “I’ll keep it short and simple. To be quite honest, the entire beginning of the season, my performances have been unacceptable. I have to be better. I will be better. There’s no excuses for it.”

“He knows he needs to get better,” manager Mickey Callaway said. “We need to get better as a pitching staff. That’s just the bottom line. We need to pitch better than we are. And we will.”

With Syndergaard facing rookie righthander Dakota Hudson (five innings, three runs, 5.89 ERA) in the rubber game at Busch Stadium, the Mets had a shot at what would have been their first series win since a sweep in Miami April 1-3.

But the Cardinals scored early and often against Syndergaard, including a pair of unearned runs in the second on Paul Goldschmidt’s single after Amed Rosario’s error. Dexter Fowler and Marcell Ozuna added RBI doubles in the third and fourth.

Syndergaard (1-2) allowed eight hits and two walks, striking out five. In the second and third innings, when the Cardinals scored three and two runs, respectively, he walked a batter to begin the frame.

“The leadoff walks hurt him,” Callaway said.

The Mets’ rotation has a 5.64 ERA through 21 games, a bottom-five mark in the major leagues.

“It’s high. It is high. That’s a fact,” Callaway said before the game. “You can put any 15, 14, 12, 20 games together and it’s not going to look great. But once it’s all said and done, I really feel like we’re going to be [good].”

Rosario made two errors Sunday and has five in his past five games. With the Mets declining to carry a backup shortstop — Jeff McNeil can play there in an emergency, Callaway has said — Rosario has had to play every inning the past week since the team sent down Luis Guillorme (and almost every inning before that).

All of the Mets’ offense came from solo homers: Pete Alonso, Syndergaard, Robinson Cano and Michael Conforto. Syndergaard’s came with an assist from centerfielder Fowler, who booped the ball over the wall when he tried to make a leaping catch at the warning track in the fourth.

Conforto’s came in the seventh, right after Cano was not awarded first base when he got hit in the right hand with a pitch. It was ruled a swing, and Callaway was ejected for arguing balls and strikes.

Most days, a quartet of homers is enough for a win. Some days, even four runs is enough. But not with the way the Mets pitchers have performed lately.

“We need to start snapping out of it. It’s time,” Callaway said. “They’re going to get better, but we need to snap out of it soon, because we’re about to go play a tough series against a good team.”

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