NEW YORK — Pete Alonso hit a three-run homer in the first inning before the New York Mets fended off several rallies by the Los Angeles Dodgers and staved off elimination with a 12-6 win in Game 5 of the National League Championship Series on Friday.

The Dodgers lead the best-of-seven series three games to two. Game 6 is scheduled for Sunday night in Los Angeles.

Alonso’s homer off Jack Flaherty (1-2) provided a much-needed first punch for the Mets, who lost 10-2 in Game 4 Thursday night and were outscored 30-9 in the first four games of the series.

New York appeared on its way to an easy win when it extended its lead to 8-1 in the third, when Starling Marte (two-RBI double), Francisco Alvarez (single), Francisco Lindor (triple) and Brandon Nimmo (single) drove in runs.

But the Dodgers inched back against starter David Peterson and relievers Reed Garrett and Ryne Stanek (1-0). Rookie center fielder Andy Pages hit the first of his two homers, a solo shot, in the fourth before Jesse Winker laced an RBI triple and scored on Jeff McNeil’s sacrifice fly in the bottom half to put the Mets up 10-2.

Pages hit a three-run homer in the fifth and Mookie Betts led off the sixth with a round-tripper before Stanek and Edwin Diaz finally cooled off the Dodgers by retiring 12 of the final 13 batters. Diaz got the last six outs in a non-save situation.

Stanek earned the win after tossing 2 1/3 innings — his longest outing in 430 big-league appearances, counting the playoffs.

The Mets added insurance on another sacrifice fly by McNeil in the sixth and an RBI single by Marte in the eighth. Marte tied a postseason franchise record with four hits.

Peterson, making his first start since Sept. 29, allowed two runs on six hits and four walks while striking out three over 3 2/3 innings.

Flaherty gave up eight runs on eight hits and four walks while striking out none over three innings.