Nationals catcher Jose Lobaton makes the throw to first in vain as the Dodgers’ Carl Crawford legs out in infield single — with the bases loaded — in the sixth inning. (John McDonnell/The Washington Post)

Before his first major league start, Washington Nationals right-hander Blake Treinen walked into Manager Matt Williams’s office at Nationals Park and thanked him for the opportunity. Before this season, Treinen had never pitched above Class AA. On Tuesday, he was recalled from Class AAA Syracuse to face the star-studded Los Angeles Dodgers and pitch against two-time Cy Young Award winner Clayton Kershaw.

“I’ll give you what I got today,” Treinen told Williams.

For five innings, the hard-throwing 25-year-old from Kansas matched zeroes with the best pitcher in baseball. But in the sixth, the big right-hander and the Nationals unraveled in familiar fashion in an 8-3 loss to the Dodgers.

Treinen opened the fateful inning by misplaying a groundball from Kershaw. Adam LaRoche followed with a bobble on a grounder from speedy Dee Gordon, and the first two men had reached. Two singles later, only one solidly hit, and the Dodgers had a lead. Treinin would fail to get an out in the inning.

The Nationals’ defense faltered yet again, yielding four unearned runs. Kershaw — in his first start since late March because of a strained muscle in his back — was in command, leaving with a 4-0 lead after seven innings (and nine strikeouts), and the Dodgers added four more in the eighth off Ross Detwiler.

With Doug Fister and Wilson Ramos returning from injuries this week, the Post Sports Live crew debates whether the starting pitcher or catcher will have a bigger impact on the Nationals. (Post Sports Live/The Washington Post)

Treinen will now head back to Syracuse to continue his development as a starter. Williams wasn’t ready to announce a corresponding move, but activating catcher Wilson Ramos from the disabled list on Wednesday is a possibility.

Treinen “pitched so well,” Williams said. “He missed that first [grounder] in that last inning, and we weren’t able to get Dee at first. That kind of set up the inning for them.”

Treinen faced a tall task, but the Nationals were doomed by their defense and inability to capitalize on the few opportunities created against Kershaw. The left-hander worked out of the only two jams he got into with ease. “He was nasty,” Nationals catcher Jose Lobaton said.

Detwiler, the other option to start Tuesday, had not pitched in six days before coming on in the eighth, and the rust showed: Hanley Ramirez led the inning off with a home run to center. Drew Butera added a three-run shot to left to make it 8-0. Jayson Werth and Lobaton singled in runs in the bottom of the inning, but by then the game was far out of reach.

Treinen’s performance was the most impressive part of the Nationals’ night. The 6-foot-5, 215-pound right-hander, part of the Michael Morse trade before the 2013 season, impressed the Nationals in spring training and earned a call-up in April to pitch out of the bullpen. He continued to dazzle, allowing just one run over 62 / 3 innings before being returned to Syracuse, where the club opted to stretch him out as a starter.

On Monday afternoon, Treinen was given the news that he was due in Washington for what was expected to be a spot start.

At 7:04 p.m., Treinen jogged out to a major league mound for his first big league start. He shook hands with a child who was standing at the mound as part of the pregame ceremonies. Treinen etched a “K” and “C,” with a cross in between the letters, behind the pitching rubber. The initials were in honor of his aunt, Kim Cousin, who passed away the previous day. Treinen held down his emotions.

His adrenaline only added to his impressive velocity. Of the 10 pitches Treinen threw in the first inning, only one was below 95 mph and most were clocked around 97. His pitches also have a heavy sink, a rare combination. He breezed through the Dodgers’ order the first time. He didn’t throw his slider until his 19th pitch.

“Sometimes you see a guy throwing 97 with a little sink, but the sink that he got on the ball is big,” Lobaton said. “. . . The umpire, he was telling me, ‘You got to hold that pitch a little bit more.’ It’s not easy, 98, 97 with sink. I’m trying.”

Treinen cruised into the sixth, when Kershaw opened the inning with a soft chopper up the middle that Treinen whiffed at fielding cleanly. His recovery and throw to first base was too late. Gordon then hit a groundball to LaRoche, who bobbled it, making him late to first. Of the two plays, only Treinen was charged with an error. Carl Crawford then loaded the bases with a swinging bunt down the first base line.

“I field that ball to start the sixth there, it might totally be a different ballgame,” Treinen said. “Work on settling down and taking my time next time.”

The bases were loaded on three balls that perhaps went a combined 200 feet. Ramirez singled the first pitch he saw, and the Dodgers took a 1-0 lead. With his workload limited, Williams took Treinen out of the game at 72 pitches. Craig Stammen emerged from the dugout and the Dodgers scored two runs on a fielder’s choice grounder and soft single to left. The damage was done.

After the game, Treinen had a long conversation with pitching coach Steve McCatty and Williams in the manager’s office before the right-hander departed for Syracuse.

“He was disappointed that he gave up some runs,” Williams said. “I said, ‘That’s a pretty good lineup over there, facing a pretty good pitcher, and you held your own. You should be proud of that.’”