On April 2, 2015, Lagares and the Mets agreed to a four-year extension worth $23 million which will run from 2016 through 2019. The Mets have a $9.5 million option for 2020, with a $500,000 buyout. Lagares made the team out of spring training as the starting center fielder. On July 31, the Mets traded for Yoenis Céspedes, who would play center regularly throughout the season. Lagares moved to backup outfield role, regularly coming in as defensive substitution late in the game. Lagares finished the 2015 season appearing in 143 games batting .259./.289/.358 in 441 at-bats in 465 plate appearances while compiling 114 hits, 41 RBIs, 6 home runs, 16 walks, 47 runs scored and striking out 87 times. In the NLDS against the Los Angeles Dodgers, he hit .429 in 4 games while compiling 3 hits, 2 doubles, 1 walk and scoring 3 runs. In the NLCS against the Chicago Cubs, he hit .333 in 4 games with 2 hits, 2 runs scored, 1 stolen base and striking out 2 times. In the World Series against the Kansas City Royals, he hit .300 in all 5 games with 3 hits, 2 runs scored, 1 stolen base and striking out 1 time.