Adam Dunn, Josh Willingham and Mike Morse each belted solo home runs to carry the Washington Nationals to a 4-2 victory over the Pittsburgh Pirates on Thursday in sweeping the three-game series.

Livan Hernandez (5-3) continued his resurgence with six solid innings. He allowed two runs and scattered five hits with three strikeouts to lower his ERA to 2.28.

Washington gave him most of its support in the fourth when Dunn hit his 13th homer and Willingham connected for his 12th of the season. Dunn scored an inning later on a throwing error by third baseman Andy LaRoche for the 3-0 advantage.

With closer Matt Capps getting the night off, Tyler Clippard pitched a perfect ninth for his first career save. It gave the Nationals their first sweep of the year, making them the last team in the majors to achieve the feat.

Pirates starter Zach Duke (3-7) surrendered three hits - two earned - on eight hits over five innings to take the loss.

Pittsburgh got on the scoreboard with a pair of runs in the sixth on a double by Jose Tabata and a sacrifice fly by Andrew McCutchen. Morse, who finished with three hits, gave the Nationals some cushion in the eighth with his first homer of the campaign.