CHICAGO — As Fernando Tatis Jr. lifted his arms skyward, watching the ball soar into the left-field bleachers, San Diego’s dugout erupted in unison. Manny Machado had just launched a no-doubt home run — and with it, he had kept the Padres’ season alive.

On Wednesday at Wrigley Field, with their postseason on the line, San Diego delivered in a must-win situation. Their 3-0 victory over the Cubs in Game 2 of the wild-card series showed exactly why the Padres are built for October baseball.

“Nothing comes easy this time of year,” Machado said after the game. “You’ve got the best of the best competing right now … and this is what we play for.”

To force a decisive Game 3 on Thursday, San Diego needed clutch offense — something that was missing in their Game 1 loss. The Cubs opened with reliever Andrew Kittredge, but his outing quickly unraveled as he gave up singles to Tatis and Luis Arraez, then a sacrifice fly to rookie Jackson Merrill. By the second inning, Shota Imanaga was on the mound, and Chicago’s plan seemed back on track — until the fifth.

After a Tatis walk and an Arraez sacrifice bunt, the Cubs elected to pitch to Machado with first base open. It proved costly. The Padres’ third baseman, with a career .846 OPS against left-handers, crushed Imanaga’s pitch into the stands, giving San Diego a 3-0 cushion.

“He’s Manny Machado,” Padres manager Mike Shildt said. “He’s finding his rhythm again, and I liked what I saw from him all the way down the stretch.”

Cubs manager Craig Counsell admitted postgame the decision backfired: “The results suggest we should have done something different,” he said.

With the lead in hand, San Diego leaned on its greatest strength: the bullpen. Starter Dylan Cease worked 3⅔ scoreless innings before handing things off to Adrian Morejon, who breezed through three frames in his longest outing of the year. Then came trade-deadline acquisition Mason Miller, who electrified the crowd by hitting 104.5 mph on the radar gun — the fastest postseason pitch since pitch tracking began in 2008. He struck out the first five batters he faced and left the Cubs flailing.

Finally, Robert Suarez closed it out, inducing a game-ending double play in the ninth to seal the victory and force Thursday’s winner-take-all showdown.

“We played with an edge, with energy,” Cease said. “It was clean baseball — and that’s what it takes to win this time of year.”

For the Padres, Machado’s blast and Miller’s firepower told the story. Their backs against the wall, they showed the kind of resilience October demands. Now, it all comes down to Game 3.