Castro scored the lone run for the Cubs with his sixth home run in the eighth inning, but Washington starter Chien-Ming Wang allowed one hit over six scoreless frames to lead the Nationals to a 3-1 win Tuesday night.
Castro has homered in consecutive games and has scored a run in 10 straight. The 21-year-old shortstop is hitting .463 with three home runs during a nine-game hitting streak.
"He's amazing. When you got a guy that has that kind of a swing and squares up that many balls and now he is starting to hit the ball out of the ballpark. Hopefully he won't change a thing in his approach. He's really put together a really offensive year so far and it may not be over, which is great," said Cubs manager Mike Quade.
In his third start — and first on the road — after missing more than two years following shoulder surgery, Wang (1-2) won for the first time since June 28, 2009, against the New York Mets as a member of the Yankees.
The Cubs have lost consecutive games after their season-best win streak ended at seven.
Nationals closer Drew Storen pitched a scoreless ninth for his 30th save in 34 opportunities.
After striking out eight batters in the first five innings, Cubs starter Matt Garza (5-9) was tagged for two home runs in the sixth. He allowed three runs and six hits in six innings. He finished with nine strikeouts and two walks.
Wang didn't allow a hit until pinch-hitter Tony Campana, who initially tried to lay down a bunt, led off the sixth with a hard liner off Morse's mitt at first. Campana beat out second baseman's Danny Espinosa's throw at first with Wang covering.
"I went up there and tried to get on base any way you can, whether it be a walk, or thinking laying down a bunt and make him move around. He was pretty good today. It was moving an awfully lot. On the last one, it started at me and left it back over where I can handle it. Morse almost made an unbelievable play. I was able to use my speed and get there," said Campana.
"The last two outings, my sinker wasn't that good, so the ball wasn't getting down. That's why they got me. In the bullpen session, I was working on the release point. I think that's why I had a good outing today," said Wang through an interpreter.
Wang's performance certainly brought back memories of his 2006 and 2007 seasons with the Yankees when he went 19-6 and 19-7, respectively.
Wang effectively used his sinker, while issuing two walks and hitting a batter with one strikeout.
In his last start, Wang gave up six runs, two earned, in five innings against the Braves, but Nationals manager Davie Johnson was encouraged. In his season debut, Wang was tagged for four runs in four innings against the Mets on the two-year anniversary of his shoulder surgery.
"No doubt about it. He was really sharp tonight. I don't know how many groundballs they hit, maybe one or two in the air. Just a magnificent performance. He was ready to go out there and pitch some more," said Johnson.
With one out in the sixth, Morse hit a tape-measure shot off Garza to give the Nationals the lead. The ball cleared the batter's eye in center for Morse's 20th of the season.
After a single by Jayson Werth, Gomes hit a two-run homer into the bleachers in left to give Washington a 3-0 lead. It was Gomes' second homer since being acquired from the Reds in a trade on July 26 and 13th this season.
"He (Garza) threw the ball well. He's been up against it a lot. He's thrown the ball extremely well," said Quade. "It's tough when you make two mistakes and you struggle to win the game.
NOTES: Cubs RHP Rodrigo Lopez, who is scheduled to start Wednesday against the Nationals, is 1-3 lifetime against Washington with a 4.62 ERA. ... LHP Ross Detwiler is Wednesday's scheduled starter for the Nationals. The 25-year old lefty is winless on the road in nine career starts. The former first-round draft pick is 0-7 lifetime away from home. ... Cubs 3B Aramis Ramirez was a late scratch because of lower back spasms. ... Nationals 3B Ryan Zimmerman extended his hitting streak to 17 games.