Stephen Strasburg struck out 12 in seven innings Wednesday. (John McDonnell/The Washington Post)

CHICAGO — Daniel Murphy found out Stephen Strasburg was starting Game 4 on Wednesday when his wife texted him. Bryce Harper found out when he showed up at Wrigley Field. Jayson Werth found out when he checked the lineup card and saw Strasburg’s name on it. They all had a similar response.

“I was like, ‘Okay, here we go,’ ” Werth said.

Strasburg didn’t know he was starting — and ultimately saving the Nationals’ season — until Wednesday morning. He went to bed Tuesday sick. He woke up still under the weather but feeling better — not great, but good enough to call pitching coach Mike Maddux to tell him he wanted to pitch with the season on the line.

“Just give me the ball,” Strasburg implored.

Nationals brass obliged, and Strasburg went on to pitch the game of his life, striking out 12  — a franchise playoff record — over seven scoreless innings in Washington’s 5-0 win five years after his infamous shutdown. Strasburg has allowed earned runs in one of his previous 66 innings and hasn’t allowed one in the postseason. After striking out 10 in Game 1, Strasburg is the third pitcher in National League history with 10-plus strikeouts in a single postseason. Bob Gibson and Sandy Koufax are the other two.

“For him to be able to cowboy up tonight and do his job . . . shows how much of a great teammate he is,” Harper said. “Just a warrior, to be able to go out there and throw that gem that he did for us.”

Said Nationals first baseman Ryan Zimmerman: “I don’t think it told us anything we didn’t already know. When he’s healthy and he’s on the mound, he’s one of the best, if not the best, pitchers in the game. To have him come out and do that in a spot like that was obviously huge.”

A day earlier, Strasburg didn’t think his chances of pitching in Game 4 were high Tuesday night after the Nationals decided Tanner Roark would take the ball, setting off a storm of confusion, speculation and derision in the sports world. His mind was on checking into the team’s new hotel — the one they stayed in the previous two nights couldn’t accommodate them for a third — and getting to sleep. Antibiotics weren’t helping. He was feeling crummy.

“Stras was sick all week,” Harper said. “I knew that. He came in the other day and his face was the color of that carpet.”

The carpet to which Harper referred was green.

“It was a challenge,” Strasburg said. “It seemed like once we got here, you know, I got hit pretty hard with this virus. It seemed to suck the life out of me every single day.”

Nationals Manager Dusty Baker said Strasburg took intravenous fluid and other anti-inflammatories, but the 29-year-old Strasburg attributed his health improvement to a switch in antibiotics. He said the toughest challenge during the game was staying warm between innings. Other than that, it was business as usual as he looked like the pitcher who has been muzzling lineups since coming off the disabled list since mid-August.

“Whooo, man, he was good,” Murphy said. “How many punch-outs did he end up having? Just, change-up any time. Fastball was electric. He was able to get back in the count with the curveball and throw it for the kill. He had it all working tonight. It was fun to watch.”

As for the whirlwind of criticism and second-guessing the Nationals’ initial decision made Tuesday night, Strasburg said he didn’t pay attention. He was sleeping for most of it. He insisted didn’t have anything to prove anyway — at least not to outsiders.

“Not to you guys, no,” Strasburg said. “No, you guys create the drama. But I know, like I said earlier, I have faith in every other guy in this clubhouse and I know the coaching staff feels the same. So we’re in it together, and when one guy goes down, you have to trust that the other guy is going to pick up the slack.”

More on the Nationals:

Nationals likely to tap Tanner Roark or Gio Gonzalez for Game 5 start vs. Cubs

Stephen Strasburg, Michael A. Taylor put Nats on their backs and force Game 5

D.C. Sports Bog: Best and worst moments from Game 4 of the NLDS

Fan favorite and former Nat Michael Morse will throw out Game 5’s first pitch

Dusty Baker offered hitless Trea Turner some words of wisdom before Game 4

Svrluga: Stephen Strasburg and Nationals nearly committed biggest error of the season

Former MLB players teed off on Strasburg before plans changed