Mets starting pitcher Noah Syndergaard (34) delivers during the third...

Mets starting pitcher Noah Syndergaard (34) delivers during the third inning of a baseball game against the Washington Nationals on March 30, 2019, in Washington.  Credit: AP/Nick Wass

WASHINGTON — After Noah Syndergaard’s “mediocre” — his own word choice — season debut against the Nationals on Saturday, the righthander and his manager identified one primary issue: Syndergaard’s slider.

“He didn’t have his plus-plus slider today, with the location at least, today,” Mickey Callaway said. “So that kind of hurt him a little bit. But he battled. Great lineup, these guys put pressure on you, he went out there and kept us in the game. Did exactly what a starter should do.”

Syndergaard got through six innings and gave up four runs and seven hits in the Mets’ 11-8 win. He struck out seven and walked none.

Failing Sydnergaard: his trust of his slider and the way he was gripping it. That was a problem on and off throughout spring training, too, he said.

“My slider really sucked today. I could not get any feel for it,” Syndergaard said. “It’s not a physical thing in terms of my slider. It’s more of a mental thing — trusting the grip and throwing it. Right now I feel like I’m trying to aim it in there and try to miss bats with it.”

The plus side to Syndergaard’s outing was picking off speedy Victor Robles at first base in the fifth inning. Getting better at controlling the running game has been a focus for Syndergaard’s for years, and Callaway believes he has made meaningful improvements in that area.

Last year, Syndergaard’s windup was such that he was tipping off baserunners when he was going home and when he was throwing to first. This year, that’s gone.

“Noah’s in a much better spot than he was last year,” Callaway said.

Injury updates

Todd Frazier (strained left oblique) played four innings at third base and went 0-for-4 in a minor-league intrasquad game in Port St. Lucie, Florida. Callaway isn’t sure how long it will take for Frazier, who did not play in any spring training games, to be ready.

“That’s something that’s going to be a lot on him, to let us know,” he said. “Talked about it extensively. Want to make sure he’s 100 percent health-wise and preparedness-wise.”

Also on the back fields at First Data Field, Travis d’Arnaud caught nine innings for the first time since Tommy John surgery last April. He went 1-for-3.

Extra bases

Brandon Nimmo (0-for-7, six strikeouts) is the last Mets regular without a hit. He does have two walks. . . . Pete Alonso said of life the last few days: “This is the most fun I’ve ever had playing baseball. This is fantastic. I feel blessed and I’m living the dream right now. I’m having a blast out there. It’s really fun.”