WASHINGTON -- New York Mets manager Terry Collins made it clear: Outfielder Juan Lagares will be in the starting lineup on Sunday.

Lagares broke out of a slump with two hits and three RBIs, and Bartolo Colon allowed two runs in eight innings as the Mets beat the Washington Nationals 5-2 on Saturday, the Mets' first victory over their division foes in the last 10 games.

Lagares, mired in a 5-for-27 slump entering the game, hit an RBI single in the first inning and a two-run home run in the third to give the Mets a 5-0 lead.

"This kid works very hard to try and get better," Collins said of Lagares, who had seen little playing time in the past few days. "He had a good game. That is why we put him in there."

Lagares robbed Washington right fielder Jayson Werth of a possible home run with a leaping catch up against the wall in center in the sixth before a sellout crowd of 41,225.

"I am not surprised by anything he does defensively. Not a thing," Collins said of Lagares.

"I did not think he had the ball," Colon said.

On Friday night, Werth made the final out of the game with a catch on a potential game-tying home run ball hit deep to right by Mets second baseman Daniel Murphy.

Rookie first baseman Eric Campbell, who had two hits and three RBIs in his fifth big-league game, had a two-run single in the first to give the Mets a 2-0 lead against Washington starter Gio Gonzalez (3-4), who has allowed 12 runs in his last two starts.

Campbell, who made his big-league debut on May 10, is 5-for-11 with six RBIs in the big leagues.

"He is a good offensive player. He can play any position on the field. He gets big hits," Collins said.

Ian Desmond, who also had two hits, slammed his sixth home run of the season -- a two-run shot in the fourth -- to pull the Nationals to within 5-2 against Colon (3-5).

"It's a work in progress," Desmond, who is hitting .228, said when asked if he is coming out of rough early start at the plate.

Colon, 40, was still hitting 93 mph on the stadium radar gun in the eighth inning. He allowed two runs and five hits in his longest outing of the season.

Jenrry Mejia, a former starter, pitched the ninth for the Mets and recorded his first save of the season in his third outing out of the bullpen.

Mejia allowed a leadoff single to Werth but struck out second baseman Danny Espinosa for the final out with a runner on base.

Collins said Friday that Mejia has not pitched back-to-back games in four years. Any chance he is used in back-to-back games after the save Saturday?

"We have to find out," Collins said Saturday. "I will find out tomorrow how he feels."

Gonzalez, who gave up seven earned runs in his last start May 11 at Oakland, needed 37 pitches to get out of the first inning. He allowed seven hits and five runs before Craig Stammen took over in the fourth.

"I didn't give any spark to the game," said Gonzalez, who sidestepped questions about a possible injured shoulder. "I was up in the zone the whole time. You have to keep grinding through it."

Collins said, "It was not his day. He did not have his crisp stuff. Fortunately we got to him."

Stammen retired the first eight batters and picked up his first hit of the season, a double to right in the fifth, and went four scoreless innings.

"He's impressive every time he goes out there," Desmond said of Stammen, who lowered his ERA to 2.52. "He comes in and humbles them, for the most part. We all appreciate the work he puts in."

NOTES: The scheduled starters for the series finale Sunday are Mets RHP Zack Wheeler (1-3, 4.53) against Washington RHP Jordan Zimmermann (2-1, 3.59). ... Washington is 18-1 when scoring four runs or more and 4-19 when held to three runs or fewer. ... The Mets have scored in the first inning in 10 of their last 15 games. ... Washington first basemen entered play Saturday with the third-highest OPS in the majors. Starters at that position have been Adam LaRoche (31 starts), Tyler Moore (nine) and Kevin Frandsen (two).