MIAMI – Pedro Martinez pitched seven solid innings, Doug Mientkiewicz hit his first career grand slam, and the Mets routed baseball’s stingiest pitching staff, beating the Florida Marlins 10-1 last night.

Carlos Beltran homered and drove in three runs for the Mets, who scored seven runs in the second inning against former teammate Al Leiter (0-2).

The Mets won a Martinez-Leiter matchup for the second time in six days. Martinez (2-0) allowed three hits and one run, retiring 13 in a row during one stretch, and snapped Florida’s four game winning streak.

The drubbing was something new for the Marlins, who gave up no more than four runs in any of their first 15 games. Their team ERA soared from 1.88 to 2.38, still the best in the major leagues.

A crowd of 27,674 had little to cheer about on Al Leiter souvenir poncho night – although there was a chant of “Pedro! Pedro!” by transplanted New Yorkers in the seventh inning. Martinez walked none and struck out eight, giving him 38 strikeouts and four walks in 29 innings.

Leiter walked five and hit a batter, and allowed five hits and eight runs in three innings, hiking his ERA from 2.55 to 5.66.

The Marlins gave up a season-high nine walks, leading to five runs. The Mets’ second-inning eruption included three walks, two scratch hits, two other singles, two stolen bases by Cliff Floyd, and Mientkiewicz’s slam.

Floyd and David Wright walked to start the second, and Ramon Castro reached on a bunt single when Carlos Delgado charged to field the ball and left first base uncovered.

Mientkiewicz pulled a 2-2 pitch for his third home run and a 4-1 lead.

Victor Diaz walked, took second on a sacrifice, and scored on Jose Reyes’s single. After Kaz Matsui singled, Beltran hit a sacrifice fly, and Floyd’s broken-bat single scored the seventh run.

Floyd batted twice in the second, reached each time, and stole second – his first steals this season.

Beltran hit a two-run homer in the fifth off John Riedling, making his Marlins debut after missing the first 2 1/2 weeks of the season with a strained right shoulder.

Two innings later, the Marlins lost another reliever when Antonio Alfonseca hurt his pitching elbow and walked off the mound with a count of 2-1 on the leadoff batter in the seventh. He’ll undergo an MRI today.

Florida’s Juan Pierre led off the first with a double, took third on a sacrifice and scored on Delgado’s groundout.

Marlins pitcher Dontrelle Willis pinch hit for Leiter in the third inning and struck out on three pitches. He went 3-for-8 as a pinch hitter last season.