Guzman fell a home run shy of the cycle, Adam Dunn homered in his third straight game and the Nationals tied a season high with their fourth straight win, 5-4 over the Florida Marlins on Wednesday night.
Ryan Zimmerman and Ronnie Belliard also homered for the Nationals, who have won 10 of 16. Washington has won the first two games of this series after dropping the first nine meetings with Florida this year.
"It's good for them to realize that we can win these close games," Nationals interim manager Jim Riggleman said. "It's been tough for us to win close games."
Washington has won three consecutive series, beating the Mets, San Diego and now Florida. Starting pitcher John Lannan said the Nationals are gaining more confidence. They scored six in the eighth to rally for a 6-4 victory in Tuesday's game.
"We definitely wouldn't have won these last two games earlier in the season," Lannan said. "Our attitude's changed, and it's a good sign. We're finishing this year strong. We know we can compete."
Riggleman said there was never a question about the team's hitting. The Nationals just weren't getting timely hits.
But they've been doing more of that lately. Guzman finished 3 for 4 with two RBIs. He had an RBI double in the third plus a run-scoring triple in the fourth that gave the Nationals a 5-1 lead.
Sosa came on in the seventh and, after giving up a two-run single to Dan Uggla that made it 5-4, got the next four batters.
MacDougal then retired the side in order in the ninth to earn his 10th save.
"They're a very dangerous offensive team, but I think they are most improved pitching-wise," Florida manager Fredi Gonzalez said. "I think their pitching has stabilized a little bit. The bullpen has improved a little bit."
Uggla hit a solo homer for the Marlins in the second inning and finished with three RBIs. But the Marlins missed on a number of scoring chances, stranding eight.
Nyjer Morgan continued to give the Nationals a spark from the leadoff spot. He went 1 for 2, walked twice, stole two bases and scored two runs. Five of the Nationals' eight hits went for extra-bases.
The Nationals took a 2-0 lead in the first when Zimmerman and Dunn homered on consecutive pitches off Florida starter Rick VandenHurk (1-1), who gave up all three homers. Zimmerman sliced a homer just inside the right-field foul pole, and Dunn followed with a long shot to right-center.
Belliard homered leading off the fourth.
"Winning fixes a lot of things," Dunn said. "We've been playing good the last couple of weeks, and hopefully we can continue that the rest of the season."
Guzman extended his hitting streak to 12 games. ... Jorge Padilla made his major league debut after playing 12 years in the minors, flying out while pinch-hitting for Lannan in the sixth. ... Uggla has reached base in eight of his first nine plate appearances in this series, getting five walks and three hits. ... Despite these two losses, the Marlins are 23-5 vs. Washington since the start of 2008.