If his major league debut seemed like a dream come to life for Braves pitching prospect Matt Wisler, then his second start Thursday must have felt like a jarring alarm clock. And a reminder that baseball at the highest level is extremely difficult.

Wisler gave up six runs — four earned — in the first three innings, and the Braves’ defense faltered while its Freddie Freeman-less offense continued to sputter, in a 7-0 loss to the Washington Nationals to complete a series sweep at Nationals Park.

It was sixth consecutive win for the National League East leaders and their eighth consecutive win against the third-place Braves, who fell to five games behind Washington and 1 1/2 games behind New York.

“Today we didn’t give young Wis a chance,” said Braves manager Fredi Gonzalez, referring to errors that allowed an unearned run in each of the first two innings as the Nationals took a 3-0 lead. “We put him in situations where he was always in trouble, never gave him a clean inning, an opportunity to get out of a jam.

“We weren’t real pretty to watch today, let’s put it that way.”

There were no fielding mistakes involved in the three-run third inning, when the Nationals got four hits, including a Yunel Escobar double and Ian Desmond’s two-run homer on a belt-high, 1-2 fastball.

Wisler (1-1), who limited the Mets to six hits and one run in eight innings of his debut win, said the early defensive gaffes Thursday didn’t put any added pressure on him.

“I just didn’t execute today,” the 22-year-old right-hander said. “My fastball command wasn’t as sharp as it needed to be. The ball just stayed up. The Desmond home run, a 1-2 or 0-2 fastball, it’s supposed to be down and away. I just left it up. Just made some bad pitches today.”

The Braves scored only two runs in the three-game series and have scored 13 runs in seven games since Freeman left the lineup with a bruised wrist.

“Just didn’t hit,” said Braves leadoff man Jace Peterson, who was 0-for-4 with two strikeouts Thursday and 0-for-13 with one walk and six strikeouts in the series. “Me, personally, I didn’t hit. Just a rough series.”

The Braves are cautiouisly optimistic about getting Freeman back around July 3, when he’s eligible to return.

“(Freeman) is a great player,” Peterson said. “We’d love to have him, he makes a big difference for us. But at the end of the day, he’s not here and we’re still capable, we just need to play.”

Six days after Wisler excelled against the Mets, he got knocked around by a Nationals team as hot as the Mets were cold. Wisler gave up four extra-base hits, threw 46 strikes in 75 pitches, and had no strikeouts or walks against a Nationals lineup that was without Bryce Harper (leg cramp) and Anthon Rendon (sore quad).

“When you have a young kid on the mound, you’ve got to give him every opportunity to get him through clean innings,” Gonzalez said. “Till he gets that experience of covering up mistakes, covering up errors. Right now, he’s not there. The other night it was his first start, we played really good defense and helped him. We didn’t do that today.”

Doug Fister (3-3) allowed four hits and one walk in seven innings to extend a streak to 41 1/3 scoreless innings by Washington starters.

The Braves came to Washington two games behind the division leaders and hoped to cut into that deficit. Instead, they’re now five games back, facing a three-game series in Pittsburgh against a team that was 22-12 at home before Thursday.

In his debut against the Mets, a 2-1 win, Wisler joined John Smoltz as the only Atlanta Braves pitchers to allow one or fewer runs in eight or more innings in his major league debut.

The Mets entered Thursday with a seven-game losing streak in which they had batted .159 and scored a total of nine runs. The snapped that with a 2-0 win Thursday against Milwaukee. Contrast that with the Nationals, who’ve hit .314 with 31 runs in a six-game winning streak in which their pitchers have allowed only five runs (0.80 ERA).

Wisler’s debut began with a strikeout of Curtis Granderson. His second start began with a single by Denard Span, who advanced on an error on the play by right fielder Nick Markakis, ending his record streak of 398 errorless games.

One sacrifice bunt later, Span scored on a Yunel Escobar ground out. The Nationals added two runs in the second inning on a pair of doubles by Wilson Ramos and Michael Taylor and a throwing error by third baseman Kelly Johnson.