WASHINGTON -- Nine and a half months ago, left-hander MacKenzie Gore and shortstop CJ Abrams were involved in one of the biggest Trade Deadline deals in baseball history. Traded from the organization by which they both were drafted, they became part of a new club’s long-term future.

The young prospects faced their former team for the first time at their new home ballpark on Tuesday night, as Washington opened a three-game set against San Diego with a 7-4 loss at Nationals Park. Abrams already had played against the Padres at Petco Park two weeks after the trade last August, but the series opener was Gore’s first matchup with his former organization; he was sidelined by left elbow inflammation at the time of the trade.

“It wasn’t about me; this was trying to come in here and win a game,” said Gore. “But it was fun. When you know guys, it was fun to compete against them.”

Gore pitched 4 2/3 innings and allowed three runs on seven hits and four walks while picking up five strikeouts. The 24-year-old was tested in the first inning: the opening at-bat of the night was a six-pitch battle against Fernando Tatis Jr. that Gore won when Tatis swung through a 98.8 mph fastball -- the hardest-thrown pitch of Gore’s career. But Gore couldn’t hold back Juan Soto, his trade counterpart, who lined a single then came around to score on Xander Bogaerts’ two-run homer one batter later.

Gore held the Padres scoreless in the next two innings. But the fourth inning began with a first-pitch home run by Brandon Dixon, marking the first time this season that Gore has allowed multiple homers. After Gore issued a two-out walk to Jake Cronenworth with Soto on second in the fifth, manager Dave Martinez made the call to the bullpen for righty Andrés Machado.

“Just not executing pitches when I need to,” said Gore, who has not gone six innings in any of his past three starts. “There’s some good in all these starts. But just consistently, I’m not executing pitches. So I’ve got to be better. This was on me tonight. It’s tough to win when the starter goes 4 2/3, so I just have to be better.”

From the opposite side of the field, though, the Padres could see the tools that helped the lefty record double-digit strikeouts twice in 13 starts last season.

“He's pretty good,” Padres manager Bob Melvin said. “We were lucky to get him on the run early there and get the home run off him. But he's got strikeout stuff. Hearing the guys talk about how his stuff plays when they come back [to the dugout], fastball's on you, it's on top of you, it's top of the zone with good extension. And then obviously he has two good breaking pitches.”

Against the slugger for whom he was traded, Gore recorded one strikeout and allowed two singles. But Soto had the last laugh, homering off Erasmo Ramírez in the seventh. It was his 50th home run at Nationals Park, but his first as a visitor.

“It’s not MacKenzie against Soto,” Martinez said. “It’s kind of MacKenzie being ours now and not with the Padres.”

Not long after Gore’s exit, Abrams, 22, added his mark to the game in the bottom of the fifth, going deep off his former teammate, right-hander Yu Darvish, to bring the Nats within one run. Abrams’ fifth home run of the season, which traveled a Statcast-projected 393 feet at an exit velocity of 107.2 mph off the bat, came before Lane Thomas went deep as well, as the back-to-back homers tied the game at 3-3.

“[Abrams] is a shortstop with power,” said Melvin. “He's got speed. Still at a young age, he looks very confident out there. He's always been a real confident player. I think that's one of his best attributes, is he always thinks he's going to get a hit. He always thinks he's going to make a play."

Abrams joins Jeimer Candelario as the second Nationals player to homer off his former team in as many series.

“Not much different,” Abrams said of his emotions homering against the Padres compared to homering against other clubs. “Probably a little more extra sauce on it, but it’s always fun.”

It wasn’t long ago that both Abrams and Gore, both former top-10 picks by the Padres, were ranked as San Diego’s top prospects at different points leading up to their Major League debuts. Now, they are fulfilling that potential 2,300 miles away wearing a new team’s colors.

"They have really bright futures,” Melvin said.