NEW YORK — If there really is something to that every-other-year thing, the San Francisco Giants must not be taken lightly.

Bruce Bochy’s late-arriving team defeated the Mets 3-0 in the National League Wild Card game at Citi Field on Wednesday behind the magnificent pitching of left-hander Madison Bumgarner and a three-run home run in the ninth inning by former White Sox third baseman Conor Gillaspie to advance to the National League Division Series against the Cubs.

The every-other Giants won the World Series in 2010, 2012 and 2014, which lines them up for another one this fall. The Cubs, with a major-league best 103 wins, are favored to win it all even though they haven’t even attended a Fall Classic since 1945 (which they lost). But the Cubs will have to get past one of the dangerous teams in baseball in the NLDS, which begins Friday at Wrigley Field, to have a chance.

The Giants reminded everyone, including a silenced crowd of 44,747, just why Wednesday night. Despite their 30-42 record after the All-Star break, they are that team nobody wants to face in the postseason, especially in a best-of-five series. They swept the Dodgers and won their last four regular-season games to get to the wild-card game, have dangerous starting pitching Bumgarner — who pitched a four-hit shutout — and have a bona fide No. 1-type starter in Johnny Cueto fresh and ready to pitch Game 1 of the NLDS. Lefty Matt Moore, the likely Game 2 starter, and right-hander Jeff Samardzija, the former Cub, round out a quality top four.

The Giants have more deep playoff experience than most Cubs, and they feel like they’re playing with house money now that they recovered in the nick of time to make the postseason.

“I like our chances,’’ Bumgarner said. “I’ll go to battle with these guys any day.”

Bumgarner, a postseason behemoth with a 8-3 record and 1.94 ERA in 15 postseason games (the third-lowest in major league history with a minimum of 10 games started, has not allowed a run in his last 23 postseason innings. He will likely start Game 3 against the Cubs’ Jake Arrieta in San Francisco.

Bumgarner outdueled the electric Noah Syndergaard, who struck out 10 with an upper-90s fastball and low-90s slider while walking three over seven innings. Syndergaard was the first Met to open a postseason game with five scoreless innings since Jerry Koosman in Game 2 of the 1969 World Series, not allowing one until Denard Span singled in the sixth. The only other hit against him was an infield single by Pagan in the seventh.

But Bumgarner outlasted him, and got his reward when Gillaspie connected on a fastball and delivered a three-run homer against Mets closer Jeurys Familia in the ninth. Familia the majors with a club-record 51 saves and allowed only one home run.

“You know, I’d be lying to you if I said I had the words to describe that moment,’’ said Gillaspie, who was designated for assisgnment by the Sox in July, 2015 to make room on the roster for right-hander Matt Albers. “Absolutely incredible, I guess, is the best I can do.’’

Gillaspie was starting at third base for injured All-Star Eduardo Nunez (strained hamstring).

“I don’t know what I was thinking,” Gillaspie, a serious, introspective sort who showed rare emotion with a fist pum as he rounded the bases. “Normally I’m not a fired-up guy. I let some frustration out from the first six innings with that swing.”