Fister allowed one run and two hits with a walk in two innings, his first game since Detroit traded him to the Nationals in the offseason.
''Overall, not bad,'' he said. ''Obviously, there are still some things I need to work on. The biggest thing was my command. I felt a little erratic out there.''
''I'm trying to get to know myself again this year. A lot of it is just fine-tuning the sinker.''
Fister, who went 14-9 with a 3.67 ERA for the Tigers last season, was happy to make his first start for his new team. It was especially important to work with his new catcher, Wilson Ramos.
''I think we're pretty well already on the same page,'' Fister said. ''He caught on very quickly. We talked a little bit (throughout camp) but a lot of it comes from game experience. That's something that today we were able to do and kind of get to know one another.''
Adam LaRoche hit a two-run homer for the Nationals. Jeff Kobernus and Zach Walters each had an RBI triple and Wilson Ramos had two hits and an RBI.
Ed Lucas hit a solo home run for the Marlins.
Marlins: Brad Hand, in contention for the No. 5 starting spot, gave up one run on two hits while striking out two in two innings. He retired the Nationals in order in the second inning.
Nationals: Right fielder Jayson Werth's name appeared in the lineup early Sunday morning, but by the time the game started he was a late scratch. Manager Matt Williams said Werth had felt a strain in his right biceps while working out Saturday and then felt it again Sunday morning. Werth has yet to play this spring.
''He's a little tight in there from working out,'' Williams said. ''We're going to push him (back) a day or two. But he's fine. No worries. It's just precautionary.''
Nationals right-hander Ryan Mattheus is still rehabbing from cartilage inflammation in his chest, and is hoping to resume throwing in a few days.
''We're getting close,'' the reliever said.
Outfielder Bryce Harper was already scheduled to have a day off. But when he came to the park exhibiting flulike symptoms, the club sent him home.
Marlins: Right-hander Henderson Alvarez, who was scratched from Sunday's scheduled start against Washington because of an infection in his shin, could be back in time to pitch Friday against St. Louis.
FERNANDEZ GETS NOD
It came as no surprise when Marlins manager Mike Redmond said Jose Fernandez would start on opening day when Miami hosts Colorado on March 31.
The 21-year-old Fernandez, who went 12-6 with 2.19 ERA last season, will be the youngest opening day starter in Marlins history.
''I know he's excited about it,'' Redmond said. ''When you think about how far he's come in the last year, from maybe slated to going to Double-A to starting the season in the big leagues to being Rookie of the Year. That's a pretty amazing year, and it just keeps going. Opening day starter ... it's a day he'll remember for the rest of his life.''
Non-roster reliever Henry Rodriguez arrived in camp Saturday night after finally resolving his visa issues. The Venezuelan native is expected to join the team for workouts on Monday. ... Reliever Carlos Marmol returned to Venezuela on Saturday to work out some of his own visa issues. Redmond said Marmol could rejoin the team Monday night, or perhaps a day or two later.