CHICAGO — Any sense of momentum seemed long gone when Miguel Montero faced an 0-2 count after the Cubs had blown a three-run lead.

But Montero cranked a grand slam off Joe Blanton to snap a 3-3 tie in the bottom of the eighth inning Saturday night, allowing the Cubs and their stressed-out fans to release a collective sigh. The result: a wacky 8-4 victory over the Dodgers in Game 1 of the National League Championship Series.

Montero’s slam capped a series of head-scratching moves by both sides, starting with manager Joe Maddon lifting ace Jon Lester for a pinch hitter in the bottom of the sixth with a 3-1 lead and only 77 pitches thrown.

Closer Aroldis Chapman was summoned after Mike Montgomery and Pedro Strop loaded the bases with no outs in the eighth, only for Adrian Gonzalez to foil Chapman’s escape ploy by ripping a 102-mph pitch for a two-run single to tie the game.

In the bottom of the eighth, Dodgers manager Dave Roberts elected to intentionally walk pinch hitter Chris Coghlan and stick with right-handed reliever Joe Blanton after the left-handed-hitting Montero was announced, despite left-hander Grant Dayton warming in the Dodgers bullpen.

Dexter Fowler, who made two diving catches in the third and fourth to support Lester’s six innings of four-hit pitching, added insurance by following Montero’s blast with a home run of his own off Blanton.

The Cubs can take a momentary breath as they avoided what could have been a crushing loss with Dodgers ace Clayton Kershaw awaiting them in Game 2 Sunday night.

Before Montero’s dramatics, Javier Baez helped carry the Cubs offense with savvy baserunning.

As he did in Game 1 and 4 of the NL Division Series with his game-winning hits, Baez seized the moment — this time with his legs.

Baez burst out of the batter’s box and reached second safely in the second inning as his bloop hit into shallow center field scored Jason Heyward.

After advancing to third on a wild pitch, Baez took a few steps toward home as Lester momentarily squared to bunt before pulling the bat back. As soon as catcher Carlos Ruiz threw to third, Baez sprinted home and beat the throw from third baseman Justin Turner to expand the Cubs’ lead to 3-0.

Fowler ran to the alley in right-center to make a diving catch to rob Turner of a hit in the third, and then Fowler sprinted to left-center to make a more impressive catch to take an extra-base hit away from Ruiz for the final out of the fourth.

The Dodgers didn’t help their cause in the second after starter Kenta Maeda hit a single to left. Third-base coach Chris Woodward waved the slow-footed Gonzalez home, but the throw from Zobrist in left field arrived well ahead of Gonzalez for the final out of the inning.

Lester proceeded to retire eight consecutive batters and 12 of 13, with a wind-aided fly-ball home run by pinch hitter Andre Ethier the lone exception.

But the Cubs were only 1-for- 6 with runners in scoring position when Lester came up in the bottom of the sixth, so Maddon opted to summon Jorge Soler as a pinch hitter.

That promoted Lester to walk very slowly to the Cubs dugout, and Soler grounded to short with Baez at second to end the threat.

For one inning, Maddon’s decision worked as Travis Wood, Carl Edwards Jr. and Mike Montgomery combined to pitch a scoreless seventh.