Dodgers’ bullpen strategy implodes in loss to the Mets

Dave Roberts was like a puppet master in the seventh inning Tuesday night, furiously tugging the strings of the Dodgers bullpen until all the lines got crossed and his marionettes collapsed in a heap.

The manager’s third pitching change of the inning left him with what he thought was a favorable matchup, even with the bases loaded and one out: Dodgers left-hander and ground-ball specialist Scott Alexander against left-handed-hitting Michael Conforto.

The move backfired spectacularly. Alexander caught too much of the plate with a 93-mph sinker and Conforto drove it over the left-center-field wall for his first career grand slam, ending a tie and pushing the New York Mets toward a 7-3 victory in front of 45,713 in Dodger Stadium.

“We couldn’t get a ground ball there with Alexander, and Conforto put a good swing on a ball that was elevated,” Roberts said. “When you’re a sinkerballer and you’re elevating, the ball tends to flatten out and you’re exposing yourself to potential slug. That’s what happened tonight.”

The two starting pitchers, left-handers Rich Hill of the Dodgers and Steven Matz, dueled to a draw through six innings, Hill giving up two runs and six hits, striking out six batters and walking one, and Matz giving up two runs and four hits, striking out six and walking three.

With the score tied 2-2 and Hill’s pitch count at 104, Roberts turned to right-hander Yimi Garcia to start the seventh. Adeiny Hechavarria led off with an eight-pitch walk. When Aaron Altherr, who bats right-handed, was announced as a pinch-hitter, Roberts pulled Garcia for right-hander Dylan Floro.

Altherr walked to put two runners on. Amed Rosario dropped a sacrifice bunt toward third base that Floro fielded cleanly but his throw to first base was low and popped out of Max Muncy’s glove for a throwing error, loading the bases with no outs.

Floro struck out J.D. Davis with a high 95-mph fastball. On came Alexander to face Conforto, whose opposite-field slam gave the Mets a 6-2 lead and sent the Dodgers to their third loss in 13 games.

“I was trying to go down and away,” Alexander said. “The pitch was away, but it was up a little bit.”

In all, five Dodgers relievers gave up five runs on a home run, two doubles and five walks in three innings. Although the Dodgers rotation has been dominant, with a 17-2 record and 2.28 ERA since April 25, a span in which they’ve struck out 183 batters and walked 24 in 1812/3 innings, the bullpen has been spotty, with a 4.61 ERA that is the third-worst in the National League.

“The numbers don’t lie,” Roberts said. “The bottom line is we’re gonna need those guys. The starters are going deep into games and giving us a chance to win every night. I believe in those [relievers]. They’ve all had their moments. We’re still winning games, but they have to go out there and get outs.”

Dodgers catcher Will Smith had an eventful major league debut, smoking a 104-mph one-hopper off the glove of shortstop Rosario in the second inning for his first hit, doubling to left center and scoring in the seventh, and throwing out Carlos Gomez attempting to steal second in the sixth.

“He just looked composed,” Roberts said of Smith. “You would never have guessed watching him tonight that it was his first big league game.”

Sign up for our daily sports newsletter »

Smith scored on Matt Beaty’s pinch-hit single in the seventh to make it 6-3, and the Dodgers had slugger Cody Bellinger up with two on and two out, representing the tying run. But Bellinger, who hit a two-run home run in the third, flied out to left to end the inning.

The Mets won despite going two for 20 with runners in scoring position. They took a 1-0 lead in the third when Matz reached on an infield single, took second on Rosario’s single, third on Davis’ fly to deep right and scored on Conforto’s check-swing tapper to third.

Matz issued a two-out walk to David Freese in the third before hanging an 0-and-2, 78-mph curveball that Bellinger crushed to right-center field for his 20th home run and a 2-1 lead. A home run by third baseman Todd Frazier tied the score 2-2 in the fourth.

mike.digiovanna@latimes.com

@MikeDiGiovanna