MIAMI -- The New York Mets' lead in the National League East is down to four games.

They lost to the Miami Marlins 4-3 on Sunday afternoon on third baseman Martin Prado's second walk-off RBI of the three-game series.

Next up is a three-game set at the Washington Nationals, the team that was 6 1/2 games back as of Thursday morning but is now charging hard.

"We'll get Murph (Daniel Murphy) back in there (Monday). We'll get (David) Wright back. This is when you call on your veteran guys to calm things down," Mets manager Terry Collins said. "We will be ready."

Maybe so, but with one out and the bases loaded in the ninth inning on Sunday, Prado lined a sacrifice fly to left against Mets reliever Tyler Clippard. Prado fouled off eight pitches before lining his shot on Clippard's 12th pitch of the at-bat.

Mets left fielder Yoenis Cespedes made a leaping grab but his throw home could not beat pinch-runner J.T. Realmuto.

"You have to be around the game a long time to see a better at-bat than that," Marlins manager Dan Jennings said. "The pitches (Prado) fouled off -- from the fastballs to the changeups -- and then to have that type of finish was tremendous."

Collins said he was comfortable with Clippard on the mound. Before Sunday, Clippard allowed just one run in 19 2/3 innings (0.48 ERA) since being acquired by the Mets in July.

"You know Prado is going to put the bat on the ball," Collins said. "But if you want one guy out there to execute pitches in that situation, it's Clippard because he can mix it up. It was one of those classic, great battles."

Added Clippard: "The last thing you want to do there is lose the game and walk the guy. Being in that spot is tough."

Before Prado's heroics, Justin Bour tied the score 3-3 with a pinch-hit solo homer -- also against Clippard -- with two outs in the eighth. It was his 16th homer of the season and the first of his career as a pinch-hitter.

The Mets fell to 75-61. The Marlins, who have won five of their past six games, are way out of contention at 57-80 but still did damage to the Mets.

New York left-hander Steven Matz, who hadn't pitched in the majors since July 5 due to a muscle tear on his left side, allowed four hits, two walks and two runs in 5 1/3 innings. He threw 81 pitches.

However, he left with a blister on the middle finger of his left hand.

"On his last pitch, he tore his skin off," Collins said."Hopefully, he is OK."

Added Matz: "I don't think it's too bad."

Marlins right-hander Jarred Cosart, who hadn't pitched in the majors since July 4 due to an inner-ear disorder that caused dizziness and nausea, got a no-decision. He lasted 4 2/3 innings and allowed five hits, one walk and one run. He threw 88 pitches.

New York started quickly. Cespedes, the game's second batter, drilled a solo homer to left-center. It was his fourth homer in the past five games and his 30th of the season.

Miami tied the score in the bottom of the first. Second baseman Dee Gordon drew a leadoff walk, stole second, went to third on a fly out and scored on a single to left by right fielder Marcell Ozuna. Gordon has 48 steals on the season.

The Marlins took a 2-1 when catcher Jeff Mathis homered to left. It was the first homer of the season for Mathis, who entered the game hitting .123.

Second baseman Wilmer Flores hit a two-run homer with one out in the sixth inning to give New York a 3-2 lead. Flores hit a 3-1 pitch from reliever Chris Narveson out to left for his 16th homer of the season.

Bour tied the score with Miami's first pinch-hit homer of the year.

The Mets had a chance to take control in the top of the ninth, loading the bases with one out. But pinch-hitter Travis d'Arnaud bounced into a double play.

In the bottom of the ninth, Mathis struck out but reached when the ball got past third-string catcher Anthony Recker on a play that was ruled a wild pitch.

Realmuto was sent in as a pinch-runner, and he reached third on a single to right by Gordon. That set the stage for Prado.

"Martin has taken over this team as the very outspoken go-to leader in the clubhouse," Jennings said. "It's easy for these young players to follow his lead. Not only is he saying it, he's doing it."

NOTES: The Mets rested 3B David Wright. ... Mets OF/1B Michael Cuddyer (wrist) missed his third straight start but could return by Tuesday. ... Mets INF Daniel Murphy (quadriceps) missed his third straight start but entered the game as a pinch-hitter and is expected to start Monday. ... Mets 1B Lucas Duda (back) could return Tuesday. ... Marlins RF Giancarlo Stanton (fractured left wrist) said Sunday he may not return this season. When he got hurt on June 26, it was reported that he would miss only four-to-six weeks. ... Marlins SS Adeiny Hechavarria (hamstring) missed his third straight game. ... Marlins RHP Carter Capps (elbow) still feels discomfort and is not ready to return.