BINGHAMTON, N.Y. – The Portland Sea Dogs have spent exactly one month alone in first place in the Eastern League’s Eastern Division.

To remain in sole possession of the lead, the Sea Dogs will need to stop the surging Binghamton Mets on Monday afternoon in the finale of a four-game series.

Rafael Montero and two relievers combined on a four-hitter Sunday night, and Allan Dykstra and Darrell Ceciliani delivered eighth-inning home runs to help the Mets secure a 5-0 victory.

Montero struck out eight in six scoreless innings. Chase Huchingson and Jack Leathersich held the Sea Dogs hitless over the final three innings.

The Mets led just 2-0 until Dykstra led off the eighth with a home run to right. Ceciliani topped that effort with a longer two-run shot.

The three Binghamton pitchers shut down the Sea Dogs to give the Mets their second straight win over the division leaders and their 10th win in the last 14 games overall.

The teams are 6-6 against each other this season.

“Playing these guys, it’s been very competitive all the way around,” Sea Dogs Manager Kevin Boles said. “Both clubs play the game very hard and both teams have a lot of strengths on the mound with a lot of quality arms.”

The Binghamton arms had an impact on the entire Portland lineup. Every batter struck out at least once, and Mets pitchers retired 12 of the last 13 batters.

“You get your work in (today) and you get ready to play,” Boles said. “Short-term memory, and you get ready to move on.”

The teams were locked in a 2-0 game into the bottom of the eighth for the second straight night.

Unlike the Sea Dogs, who let their late lead get away in Saturday’s extra-innings loss, the Mets were able to expand their lead.

Montero (5-3) struck out eight and did not allow a runner to reach third after Shannon Wilkerson singled and stole two bases to start the game.

“It was our first outing that we’ve seen him, and he can throw any pitch and any point in the count. … He is very impressive,” Boles said of Montero, a 21-year-old right-hander who is regarded as one of the New York Mets’ top prospects after going 11-5 last season.

Binghamton Manager Pedro Lopez said that other than adjusting his pitch sequence to reduce the number of pitches he needs to get through innings, there is little more to ask from Montero, who has already gone to Triple-A Las Vegas for one start.

“He doesn’t throw anything over the middle of the plate,” Lopez said. “Everything he throws is on the corners.”

Knuckleballer Charlie Haeger (1-2) struggled with his control early, then settled in and worked into the eighth inning before leaving with nobody out after allowing the two home runs. Earlier, three wild pitches helped the Mets score twice, including one unearned run.

“I felt like we had good at-bats,” Lopez said. “We didn’t have too many hard-hit balls, but we didn’t chase a lot of pitches.

“Some of these guys had never seen a knuckleball before.”