NEW YORK -- Lucas Duda started off August the same way he finished July -- on a tear.

The slugging first baseman provided all of the offensive power in the New York Mets' 3-2 victory over the Washington Nationals on Saturday before 42,996, the second-largest crowd in Citi Field history.

The Mets (54-50) moved one game behind Washington (54-48) in the National League East.

Duda clubbed two solo home runs and drove in the deciding run with a double that scored Curtis Granderson, who led off the eighth inning with a double, to give the Mets a 3-2 lead.

Duda now has eight home runs in his last seven games. His opposite-field homer leading off the seventh tied the score at 2.

He's tied with Carlos Gonzalez of Colorado for most home runs since the All-Star break, with eight.

"If I knew the secret (of the streak) I would apply it," Duda said. "It's just one of those things. Sometimes you have a good month and sometimes you have a bad month. Sometimes you have a bad night and sometimes you have a good night. It is what it is."

Washington manager Matt Williams made the game-changing decision to intentionally walk new Met Yoenis Cespedes in front of Duda in the eighth. Duda promptly hit a 1-2 pitch off Matt Thornton off the base of the wall in left for the deciding run.

"I was surprised they walked me," Cespedes said through an interpreter. "Who knows what would have happened if I actually got to take a swing? But if that was the best thing for the team, then I'm OK with it."

Cespedes, who was making his Mets debut, went 0-for-4. He started in left field and hit third after being acquired from the Detroit Tigers on Friday.

Shortstop Ian Desmond knocked in two runs for the Nationals and right fielder Bryce Harper went 2-for-4 with a run scored.

Jeurys Familia notched his 28th save and Hansel Robles (3-2) picked up the win, striking out Harper and Jayson Werth in a perfect eighth. Thornton (1-1) took the loss.

Mets starter Jacob deGrom lasted six innings, allowing two runs while striking out seven and walking one. In his previous start, a 7-2 win at Washington on July 21, deGrom had allowed two runs and three hits while striking out eight in six innings.

Washington's Joe Ross, making just the sixth start of his young career, also didn't factor in the outcome. He went seven innings, giving up four hits -- two via Duda's homers. He struck out six and walked one.

Desmond provided the Nationals with a 2-0 lead in the first inning when he cracked a broken-bat single just past shortstop Ruben Tejada with two outs and the bases loaded. DeGrom threw 31 pitches in the inning.

"It's cautious optimism, but we have to keep adding," Williams said of his team's early lead. "We got a high pitch count on him (deGrom) early and then he settled in. But we had opportunities."

Mets pitchers retired 20 of the last 22 batters from the end of third inning on. Only Harper and Ross reached base, both on singles.

Duda cut Washington's lead in half in the fourth with his 19th home run of the season, a deep drive to right-center field.

Until Duda's blast, Ross had not allowed a hit, retiring 11 of 12 Mets. Duda had been the lone baserunner, drawing a walk to lead off the second.

Right-handed batters entered the game hitting just .187 against Ross.

NOTES: Mets manager Terry Collins said 3B David Wright will stay with the team through next week, then start a rehab assignment with St. Lucie. Wright has been out since April 14 with a back injury. ... OF Yoenis Cespedes, acquired from Detroit before the trade deadline, is the 11th Cuban-born player to play for the Mets. To make room for Cespedes, who won the 2013 Home Run Derby at Citi Field, the Mets sent OF Michael Conforto to Triple-A Las Vegas. ... Major League Baseball made a scoring change in the Mets-Nationals game of July 20. Washington INF Danny Espinosa's bunt single was changed to an error by Mets P Matt Harvey, which makes both runs scored in the first inning unearned. ... Nationals RHP Max Scherzer's 9.05 strikeout-walk ratio this season is fifth-best in baseball since 1900.