Pete Alonso's three-run homer capped a five-run third inning Monday night as the visiting New York Mets rolled to a 13-3 win over the skidding San Francisco Giants.

J.D. Davis had four hits and two RBIs for the Mets, who have won three of their first four games on a six-game road trip. Jeff McNeil and Mark Canha homered, Francisco Lindor and Eduardo Escobar each had a two-run double and Patrick Mazeika added an RBI double.

The Giants have lost five straight and are 2-7 in their past nine games, a span in which they have been outscored 70-38.

Brandon Crawford gave the Giants an early lead by hitting a two-run homer off David Peterson (2-0) in the second inning, but the Mets responded by scoring five runs with two outs in the third against Alex Cobb (3-2).

Davis singled with one out before Brandon Nimmo and Starling Marte had back-to-back, two-out infield singles. Lindor blooped a ground rule double just fair down the left field line, and Alonso homered into the left-center-field bleachers on the next pitch. It was the 11th homer of the season for Alonso, tying him for the National League lead with the Colorado Rockies' C.J. Cron.

The outburst was more than enough for Peterson, who made his first start since replacing the injured Max Scherzer in the Mets' rotation. Peterson allowed two runs on three hits and one walk while striking out six over six innings. He retired the final 11 batters he faced.

Davis had an RBI double in the sixth before the Mets piled on against a trio of relievers in the final two innings. McNeil and Canha hit back-to-back homers in the eighth, when Mazeika had his RBI hit.

San Francisco outfielder Luis Gonzalez pitched for a second straight day in the ninth and gave up the run-scoring hits to Escobar and Davis.

Every starter finished with at least one hit for the Mets, who collected a season-high 18 hits on manager Buck Showalter's 66th birthday.

Tommy La Stella added an RBI single in the ninth for the Giants.

Cobb allowed six runs on 10 hits and no walks while striking out seven over six innings.