SAN DIEGO (AP) -- For the second straight outing, San Diego Padres starter Erik Johnson had a 2-0 lead in the first inning.

For the second straight outing, Johnson didn't take advantage of it.

Johnson and the Padres fell to the Washington Nationals 8-5 on Thursday night.

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Johnson (0-2), who was acquired from the Chicago White Sox on June 4 in the deal for James Shields, struggled again. He was charged with five runs, seven hits and two walks over six innings. He struck out two in his second start with the Padres.

It was the home run ball that did in Johnson has he gave up three. What adds to Johnson's frustration is that he had two-strikes on Bryce Harper, Wilson Ramos and Anthony Rendon before they hit their long flies.

"Almost all of his hits were with two strikes," Padres manager Andy Green said. "I think it's a little bit of a function of he's working predominantly one side of the plate."

Johnson and Green saw some progress.

"Compared to my last outing, I'm definitely taking more than a few steps forward," Johnson said. "I had a feel for all four of my pitches. I used them well, just a few balls left the yard.

"For me, it's just putting myself in situations where I've got to stay away from that."

Tanner Roark (6-4), who won his third straight against the Padres, worked six innings, surrendering four runs and seven hits. He walked two, with five strikeouts.

"He's a fighter," Nationals manager Dusty Baker said. "He will always battle for you."

Washington stretched its lead to 8-4 in the ninth, with Harper getting his third RBI on a single.

San Diego had the tying runs aboard against reliever Blake Treinen in the seventh, but Melvin Upton Jr. struck out.

The Nationals extended their lead to 6-4 in the seventh on Clint Robinson's sacrifice fly.

In the sixth, the Padres made it a one-run game on the speed of Upton. He singled to open the inning, then stole second and third. He came home on Christian Bethancourt's grounder, making it 5-4.

Rendon went deep in the sixth inning for his seventh homer of the season, good for a 5-3 lead.

Wil Myers, who has lobbied to be included in next month's Home Run Derby, smacked his career-high 15th homer in the fifth. His one-out laser off a 93 mph fastball pulled the Padres within 4-3.

The Nationals flexed their muscles in a three-run third inning as they forged ahead 4-2.

Harper went the opposite way for his 14th homer on the year, a two-out, two-strike, two-run shot that brought in Jayson Werth, after he singled.

Ramos gave Washington its ninth set of back-to-back homers when he crushed Johnson's full-count fastball for his second hit.

Stephen Drew's sacrifice fly brought in Ramos, who reached via a single.

The Padres struck in the first, taking a 2-0 lead.

Travis Jankowski opened with a single, which preceded a walk to Myers. Matt Kemp slapped a low pitch up the middle for an RBI single and Myers scored on a single by Upton.

TRAINER'S ROOM

Padres: RHP Andrew Cashner (sore right shoulder) could begin a throwing program on Friday.

UP NEXT

Padres: LHP Christian Friedrich (3-1, 5.37) has made the most of his opportunity as injuries and trades upended the rotation. Friedrich threw six innings of one-run ball against the Rockies in his last start, but he didn't get a decision

Nationals: RHP Joe Ross (5-4, 3.01), a former Padres first-round draft pick, is seeking his third straight win. Ross is the brother of Tyson Ross, the Padres' Opening Day pitcher who is on the DL.