Zack Wheeler’s sweet Citi Field debut went sour after one inning. The Mets prospect’s velocity went down, his command of his fastball went away, and the Nationals hitters went off, hammering him in a 13-2 rout.
Following a 1-2-3 first inning, Wheeler (1-1) struggled in a four-run second and gave up five runs in just 4 2/3 innings to lose his highly anticipated Flushing debut. Reliever Brandon Lyon coughed up six more runs in just two-thirds of an inning, and the Mets mustered just three hits off Gio Gonzalez in seven innings.
“First inning I was hitting my spots, everything was working, then I started leaving some balls up,” Wheeler said. “I’m starting to learn the hard way that you can’t get away with mistakes up here as much as you do [in the minors]. It’s a learning experience so far. That’s what your bullpen [sessions] are for: Time to get better.’’
After working during the week to keep from tipping pitches as he did in the Mets’ 5-4 loss at the White Sox last Tuesday, Wheeler hit 98 mph and put the Nationals down in order in the first. But his first pitch in the second — a 95-mph fastball — was crushed off the loge signage in right field by Adam LaRoche.
Wheeler walked Jayson Werth on four pitches, watched Ian Desmond stroke an RBI double and Kurt Suzuki fight off his 0-2 pitch for an RBI single off shortstop Omar Quintanilla’s glove. Denard Span’s RBI double to left-center made it 4-0, then Wheeler hung a 1-1 fastball to Werth for a solo shot in the third. After he walked LaRoche in the fifth, manager Terry Collins had seen enough.
“After Adam hit the first pitch of the second inning, it certainly got his attention,” Collins said. “He threw some good pitches. I thought he was down in the zone, but it certainly was not how we scripted it out to be. As I said before, he’s a work in progress. The future’s still extremely bright, the ceiling’s extremely high.’’
Wheeler — who left to applause from the crowd of 33,366 that included his family — could tell he had lost some velocity, possibly because of tinkering with his mechanics, “trying to keep my front side in, finish at the plate instead of falling off.”
But he had no answer for the more glaring issue — his fastball command.
“I’ve always struggled with my fastball command. I’ve tried tons of things, and I’ll keep trying to get it better. Once that happens, I’ll just take off,’’ said Wheeler, who agreed with catcher John Buck that he had fixed the issue of tipping pitches.
Buck said the changes weren’t mechanical and didn’t impact Wheeler’s command.
In the eighth, Lyon allowed an RBI double to Roger Bernadinia, a two-run shot to Suzuki, a two-run double to Anthony Rendon and Ryan Zimmerman’s RBI single to push it to 11-0 and see his ERA bloat from 3.45 to 5.06.
The game got so ugly backup catcher Anthony Recker took the mound in the ninth. Recker’s first six pitches were balls, and Desmond hammered his seventh into the second deck in left for a two-run blast.
“You get into a situation where you don’t want to burn any more relievers,’’ said Collins, citing Walter Alston’s mantra, “Don’t ever blow your bullpen out in a game you can’t win.’’
Tthe Mets surely weren’t winning this one. Buck hit a cosmetic two-run shot in the ninth to break up the shutout.
brian.lewis@nypost.com