Aroldis Chapman gets an eight-out save to help Chicago to a 3-2 victory over the Cleveland Indians Sunday at Wrigley Field. (Charlie Riedel/Associated Press)

We know by now that, no matter how much the Chicago Cubs intend to treat their most significant games as some sort of three-game sojourn in June, convention is obliterated by the time Halloween is near. What is required, with eight outs that must be recorded to extend the season, is the best weapon available. What was required for the Cubs on Sunday night was Aroldis Chapman, even if he had never recorded eight outs in a major league game.

Chapman doesn’t just have the hardest fastball in baseball. He is an utter outlier. But after Sunday night’s 2⅔ -inning outing to overwhelm the Cleveland Indians, he merely fits into how bullpens must be used at this time of year. With a loss, the Cubs season would have been over. There was no time for setup men. There was time only for Chapman to nail down a 3-2 victory in Game 5, to send the series back to Cleveland for a sixth game Tuesday night.

“That right there,” third baseman Kris Bryant said, “is exactly why we got him.”

It’s really that simple, and their season lives because of it. Cleveland still holds a 3-2 advantage in the series. But Wrigley Field finally got to let its hair down Sunday night. When Chapman pumped one last 101-mph fastball past Indians third baseman Jose Ramirez for the final out, what had been a rather antsy building for much of the weekend exhaled, and loudly. Finally, the Cubs fans got to “Fly the W.” Finally, they got to sing “Go Cubs Go!” at the top of their lungs following a World Series game.

The baseball season is over in Chicago. But it’s not over for Chicago.

Hint: There were only 46 states. (Gillian Brockell/The Washington Post)

[Boswell: Suddenly, it’s a Series again — and pitching gives Cubs a chance]

“I’ve never been looking forward to wanting to play the seventh game of a World Series in my life,” Cubs Manager Joe Maddon said, knowing he’d need right-hander Jake Arrieta to beat the Indians on Tuesday first. “. . . From an entertainment perspective, if you’re a baseball fan or looking to become a baseball fan, it was wonderful tonight — outstanding.”

So winter is staved off, and the wait for these two franchises for a World Series title — the Indians since 1948, the Cubs 40 years longer — lasts at least another two days. There were other pieces to this win, not least of which that the Cubs managed to get something that is essential when facing the reliever-rich Indians — an actual, bona fide lead. They built that in the fourth, first on Bryant’s game-tying solo homer, then with four more hits in the frame — a spinning squibber of an infield single from Addison Russell providing one run, a bases-loaded sacrifice fly from David Ross providing another.

“We really want to grab a lead and keep it,” Maddon said. “I mean, that’s just common sense.”

Coming into the evening, Wrigley had essentially been paralyzed since Friday night, when it hosted its first World Series game in seven decades. The Cubs couldn’t push anything across against Josh Tomlin, and when the Indians managed a run in the seventh, Cleveland put the hand to Wrigley’s throat. Of the 18 innings played here over Games 3 and 4, the Cubs had led after just one, the first inning on Saturday.

Against the Indians, it’s more important than get the lead. Two reasons Cleveland Manager Terry Francona has, rightly, been praised for his maneuvering of his pitching staff this October has been because: 1) his pitching staff has been absurdly awesome, and 2) his pitching staff has so frequently had the lead. In 108 postseason innings prior to Sunday night, the Indians had led after 68 and were tied after 22. They trailed less than 17 percent of the time.

So Francona’s strategy, which he offered in farce: “Get the lead and let them face the dominant relievers. It’s really not rocket science.”

Nor was going to Chapman when Maddon did. Because a loss would have ended the season, the manager and the closer had a conversation Sunday afternoon. This would not be, Maddon told Chapman, one of those days when he’d just be expected to zip out 15 or so fastballs in the ninth and call it a night. This was going to be work.

Chapman obliged.

“Obviously, I told him, I’m ready,” he said through an interpreter. “I’m ready to go. Whatever he needs me to do or how long he needs me to pitch for, I’m ready for.”

[Jim Harbaugh brought a glove to Game 5 of the World Series]

Cubs starter Jon Lester worked through the sixth, allowing Ramirez’s solo homer in the second and an RBI single to Francisco Lindor that made it 3-2. What got dicey for Maddon was his bridge to Chapman: right-hander Carl Edwards Jr., last seen allowing the only run of Game 3. It was Edwards’s job to get Mike Napoli leading off the seventh.

“The Napoli-CJ matchup,” Maddon said, “I like a lot.”

And yet Napoli singled. And then a passed ball moved him to second. Maddon allowed Edwards to face Carlos Santana, who hit a lazy fly ball to left.

And here was Chapman.

“I don’t think anybody ever relaxed,” center fielder Dexter Fowler said. “We were pretty high-strung, ready to go. It’s 27 outs.”

There were eight to go. The last time Chapman appeared in a game that early: May 17, 2012, when he was with Cincinnati. For Cubs fans, four-plus years ago is nothing. One hundred eight years? That’s a long time.

“There’s all kinds of drama out there,” Maddon said.

So Chapman went to work and wriggled out of the seventh, working around the fact that he hit Brandon Guyer with a pitch. In the eighth, Rajai Davis singled to first — on a play when Chapman declined to cover the bag.

“He said he thought the ball was foul,” catcher Willson Contreras said.

Davis then stole second, and an out later, third as well. But Chapman dealt with that by throwing two-strike, 101-mph heat to Lindor, which Lindor could only look at for strike three.

Maddon’s commitment to Chapman was so extensive that he allowed him to bat in the bottom of the eighth, even with a runner on base. It was his third career plate appearance. He struck out.

His ninth was comparatively uneventful. But the evening was not. The Cubs celebrated by coming back out of the clubhouse and sharing the victory with their fans.

“Why not us?” Bryant said.

We’ll see. This World Series, by virtue of having opponents that have waited generations for a title, is already in uncharted territory. Now, its participants are entering areas they haven’t been before, too. The next chance for any of that will be Tuesday, in Cleveland. It’s not winter yet.