CHICAGO — Playing in front of a raucous Wrigley Field crowd, the Cubs relied on two struggling players to help lead them to a Game 4 victory over the Milwaukee Brewers in the NLDS on Thursday, forcing a do-or-die Game 5 on Saturday in Milwaukee.

Starter Matthew Boyd and left fielder Ian Happ set the tone early for the home team, with Boyd pitching 4⅔ scoreless innings and Happ hitting a three-run home run in the bottom of the first inning to propel the Cubs to a 6-0 win.

“The guys have been carrying me all postseason, so to contribute in that moment and give us the lead was awesome for me,” Happ said after the game.

Happ entered the night hitting .095 this postseason, but that was quickly forgotten when he crushed a 1-1 fastball from Brewers starter Freddy Peralta, igniting an already rabid crowd. Throughout the first inning, seemingly all 41,770 in attendance were chanting “Fred-dy! Fred-dy!” as Peralta struggled with his command, eventually serving up a pitch over the heart of the plate to Happ.

“This crowd affected the game the last two games,” Brewers manager Pat Murphy said. “It affected the way we played for sure.”

Cubs second baseman Nico Hoerner took notice of the chants as well.

“I kind of wonder how that starts,” Hoerner said with a smile. “It made me think of the [Johnny] Cueto chants back in Pittsburgh a long time ago.”

The crowd quieted when Boyd took the mound, just five days after getting only two outs in a Game 1 loss. Questions about what he had left in the tank lingered throughout the week after his subpar September was followed by Saturday’s short outing in Milwaukee.

“I thought the first inning was just so important tonight,” Cubs manager Craig Counsell said. “[Christian] Yelich draws a walk and then he makes pitches. But just getting through the first inning was, to me, the key for Matthew’s outing.

“I know it was really important to him after Game 1 how he pitched tonight, and he gave us exactly what we needed.”

Boyd deflected questions about rebounding from Game 1, instead giving his catcher, Carson Kelly, all the credit. Kelly said the two made adjustments, getting the ball inside to righties while the adrenaline from the crowd added another mph or two on his fastball. Boyd looked more like the pitcher who made the All-Star team this year.

“This was kind of the early version we were accustomed to seeing,” shortstop Dansby Swanson said. “It was a good time for him to be really good.”

Boyd also credited the crowd, saying Thursday was “another level.” Murphy described a different pitcher than the one he saw in Game 1.

“He was on it,” Murphy said. “He didn’t leave the ball down the middle. Made quality pitches in. Dropped his breaking ball in for a strike. Made pitches when he needed to. He was fabulous.”

Boyd left after giving up 2 hits, walking 3 and striking out 6. Unlike Wednesday’s Game 3 nail-biter, the Cubs added on in Game 4. Home runs by Kyle Tucker and Michael Busch turned what was a tight contest early into an easier night for the bullpen.

It also gave the Wrigley faithful more reason to cheer.

“I’ve never seen a baseball game like that,” Counsell said of the crowd. “That was just amazing what they did tonight.”

Murphy added: “That kind of stuff emotionally can affect guys. They can start to play a little too hard. This game is a game of precision, and the Cubs’ experience and what they’ve been through. They were better in this environment for sure.”

As the longest-tenured Cub, Happ knows what October baseball looks and feels like at Wrigley Field, but it had been more than half a decade since he had experienced it. Until Thursday night, he hadn’t given those fans much to cheer about this postseason. That changed with one swing, which also changed the momentum of the series.

“To do it in this atmosphere, in this stadium, in front of these fans … they’ve been here every day,” Happ said. “It doesn’t matter if it’s Tuesday in the middle of June, they’re here. There’s 40,000 people here. To give them that experience and to hear that roar was really special.”