The Phillies felt pretty good the moment Andrew McCutchen stole home in the first inning Thursday at Nationals Park.

They hoped to sweep their first three-game series on the road since April 2018 against Tampa Bay. Remember that one? Jake Arrieta, Edubray Ramos and Yacksel Ríos got the wins at Tropicana Field. J.P. Crawford and Aaron Altherr hit the Phillies’ only home runs. On Thursday, McCutchen’s successful steal in the first put the Phillies on the board against struggling Nationals left-hander Patrick Corbin, who entered the game with a 7.36 ERA.

But then Phillies right-hander Zach Eflin struggled in the first inning and the Phillies’ offense fell silent in a 5-1 loss.

• Box score

The Phillies still won their first series on the road since September 2019. They will take it.

“We’re happy we won the series,” Eflin said. “We wish we could’ve gotten the win today. I could’ve thrown better in the first inning and kept us in the ballgame. But at the end of the day, we won the series and we’re happy about that. Regardless, we’ll have a happy flight to Dunedin and we’ll take it from there.”

Eflin started the afternoon with a 3.38 ERA in seven starts. He allowed two or fewer runs in four of his last five. His 1.6 percent walk rate ranked best in the National League among qualified pitchers. He had not allowed a home run since April 16.

But then in the span of three batters in the first inning, Eflin allowed a home run, walk and home run.

Kyle Schwarber hit a 1-0 sinker for a two-run home run to left field to give the Nationals a 2-1 lead. Starlin Castro walked and Josh Bell hit a two-run home run to right field on a first-pitch slider to make it 4-1.

“Yeah, it’s pretty uncharacteristic,” Eflin said. “I mean, I hate giving up walks. They just took advantage of it. I’m going to go out and throw a bullpen and get my location back and just keep trusting what I’m doing and be a competitor. Baseball is a funny game. It’s a game of failure and sometimes they’re going to clip you. Sometimes they’re going to miss balls right down the middle.

“The one to Schwarber was kind of middle away, a little up. I'm trying to go down and away right there and get a roll over. But I left it up a little bit and he did what he was supposed to do. … The backdoor slider to Bell kind of got a little bit more middle of the plate than I wanted. He did a good job of ambushing.”

Eflin allowed just one more run over the next five innings. He struck out nine overall.

Corbin pitched better. After he allowed an infield single to Bryce Harper with one out in the first, he allowed only three more hits over his seven innings. He struck out nine and walked none.

Corbin’s four-seam fastball averaged 92.7 mph, 1.7 mph better than it had been all season.

The Phillies noticed.

“His velocity is back,” Phillies manager Joe Girardi said. “His velocity came back his last start. It was the biggest difference. I was saying [before the game], I’m not sure which one we’re going to get: the one that’s throwing 89 mph, or the one that’s throwing 91-94 mph? And when it gets to the 94 consistently, everything gets better. His slider gets better, his changeup gets better and that’s what he did.”

It did not help that the Phillies were shorthanded. J.T. Realmuto is on the COVID-19 injured list and Didi Gregorius is resting a sore right elbow. They might have helped.

Realmuto is not flying with the Phillies to Florida, where they will open a three-game series Friday night against the Blue Jays in Dunedin. The Phillies hope Gregorius could return to the lineup sometime this weekend.

“I’m not quite sure how quickly it will turn around,” Girardi said about Realmuto’s chance to play this weekend.

It will be more difficult to beat the Blue Jays, much less sweep them, without those two.