Kyle Finnegan (1-0) struck out Jorge Alfaro to escape a two-out, bases-loaded jam he inherited from starter Max Scherzer in the fifth to earn his first major league win. Tanner Rainey pitched a 1-2-3 sixth, and Daniel Hudson earned his sixth save with a perfect seventh.
While Scherzer labored for much of his outing, Miami didn't manage anything until Jonathan Villar's RBI single in the fifth and Matt Joyce's homer a batter later. Scherzer allowed the next four hitters to reach and was finally chased when Jesus Sanchez walked with the bases loaded.
Scherzer surrendered four runs while throwing 108 pitches in 4 2/3 innings. It was the third time in six starts the three-time Cy Young Award winner allowed at least four runs.
''I believe in tough spots in the game, even when the pitch count is above 100, I can excel in those situations,'' Scherzer said. ''Unfortunately, the past couple games I haven't done that and I need to get better at that.''
Miami starter Daniel Castano (0-2) got only one out against four batters, allowing two runs. The Nationals increased the lead to 3-0 on Howie Kendrick's sacrifice fly in the third.
The Marlins' defensive sloppiness helped Washington score twice in the fourth. Kurt Suzuki and Josh Harrison opened the inning with consecutive singles, and Sanchez, a rookie, sailed a throw from right field well past third to allow Suzuki to score. Two batters later, Harrison scored when left fielder Corey Dickerson dropped Victor Robles' fly ball.
The Nationals played as the home team in the regularly scheduled opener. The Marlins will serve as the home team in nightcap, which was originally part of a July 31-Aug. 2 series in Miami postponed because of a COVID-19 outbreak that led to injured list stints for 17 Marlins players.
Marlins: LHP Caleb Smith and RHP Jose Urena both had throwing sessions Saturday at Miami's alternate training site.
Nationals: RHP Stephen Strasburg (0-1, 10.80 ERA) was transferred to the 60-day injured list, effectively ending his season. Strasburg, the World Series MVP last year, was limited to two starts and will undergo carpal tunnel surgery next week. . Manager Dave Martinez said LHP Sean Doolittle (right knee) will throw to hitters at the team's alternate training site Sunday. . INF Howie Kendrick (hamstring) was the DH, his first time in the lineup since Aug. 14.
Washington will add RHP Wil Crowe to start the second game and make his major league debut. Crowe was the Nationals' second-round pick in the 2017 draft. . Miami brought up RHP Jesus Tinoco as its 29th man. Tinoco threw two scoreless innings in the opener.
Marlins: RHP Humberto Mejia (0-1, 5.68 ERA) faces a team other than the Mets for the first time in his brief major league career when the series continues Sunday.
Nationals: RHP Anibal Sanchez (0-3, 8.50) has allowed 39 baserunners (29 hits, nine walks, one hit batsman) over 18 innings in his first four starts of 2020.
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