Only five weeks after displaying a proverbial deer-in-the-headlights look in his major league debut, Williams Perez stood atop the mound at one of baseball’s grand cathedrals Monday and performed as if he’d been there a thousand times.

Perez pitched six shutout innings, and the bullpen that’s been the majors’ worst came through with three just-good-enough innings in a 4-2 victory to open a two-game set at Fenway Park, the seventh consecutive loss for the Red Sox.

Perez (3-0) earned a win just two days after recording his first save at any level when he pitched a scoreless 11th inning against the New York Mets.

“He pitched better than what we expected, after pitching in that save situation Saturday,” Braves manager Fredi Gonzalez said. “Coming in on short (rest) there, and short again tonight. Pitching in Fenway against an American League team – I couldn’t ask for anything more. He exceeded expectations.

“But you run him out there in different situations and he always rises to the occasion.”

The Braves scored three runs in the third inning and pushed the lead to 4-0 in the seventh, then strapped themselves in for another eventful ride with their pathchwork bullpen, after Perez was replaced with his pitch count (79) creeping up against the 80-pitch limit that Gonzalez alluded to before the game.

The bullpen got it done this time. But it wasn’t a breeze. Nick Masset recorded the last two outs of the seventh inning — after left-hander Dana Eveland faced three batters and gave up a home run and a double – and Jim Johnson pitched a scoreless eighth before Jason Grilli gave up an unearned run in the ninth and converted his 17th save.

The Red Sox had runners on the corners in the ninth after a Pablo Sandoval ground-rule double and a throwing error by shortstop Andrelton Simmons, who had his throwing hand smashed by a pitch after squaring to bunt two innings earlier.

Grilli got Alejandro De Aza on a comebacker to the mound to end the game, and postgame X-rays of Simmons’ hand revealed no apparent structural damage. An all-around big sigh of relief, no pun intended.

The night belonged to Perez, who gave up five hits and two walks with two strikeouts, lowering his ERA to 2.29 in eight games (six starts). A Venezuelan rookie, he gave up four runs in one-third of an inning in that debut at Washington on May 8, and has allowed just six earned runs in 39 innings since then, for a 1.38 ERA in that impressive stretch.

Even more impressive, he’s allowed just one run in 22 innings on the road since that debut.

Light rain and 58 degrees? Noisy Fenway? No worries.

“I didn’t hear anything,” Perez said. “I was just concentrating on the game.”

Braves veteran Kelly Johnson said, “I love Williams Perez, man. I do. How cool was that? To get a save two days ago and then come back and pitch like that and get a win. I don’t think there was any doubt in anybody’s mind that that was going to happen. It’s just one of those things, it seemed like it was meant to be. … I think he’s got his gameplan, he knows what he wants to do, he’s confident, and I think he’s locked in. I don’t think he gives a rip where he is.”

As nerve-racking as it must have been for Braves fans to see a four-run lead turned over to the recently crumbling bullpen it had been even more frightening to see Simmons grimacing in pain in the top of the seventh, after the Gold Glove shortstop took a pitch from Rick Porcello off his right hand.

Simmons turned to bunt with two runners on and one out, and had his hand wrapped improperly around the bat, exposing the fingers attached to his valuable throwing arm. Gonzalez said there were ball seams visible on the fatty part between the fingers, but said the Braves were fortunate it hit there instead of directly on a finger or bone in his hand.

As Simmons was being examined by Braves head trainer Jeff Porter, the Braves challenged the foul-ball call and won, getting it reversed to a hit-by-pitch. Simmons stayed in and took first to load the bases, and Jace Peterson singled to extend the lead to 4-0.

Because of the stress of Perez’s one-inning relief stint Saturday on what would normally have been his day to throw a between-starts side session,Gonzalez said before Monday’s game that he would be closely monitored.

The Braves stuck with that plan, letting Perez get the final out of the sixth inning after he’d issued consecutive two-out walks, his only walks of the game. He threw 79 pitches (47 strikes).

Perez faced just two batters over the minimum in six innings, allowing five singles and two walks but also inducing three double-play grounder. He recorded nine outs in nine batters in the first three innings despite giving up a single in each inning.

After each of those three hits – leadoff singles in the first and second innings, a one-out single in the third – Perez got the next batter to ground into a double play.

Unlike in previous starts, Perez didn’t have to work out of multiple jams, as the Red Sox didn’t have more than one runner reach base until the sixth inning. He gave up another leadoff single in the sixth to Mookie Betts, then picked off the speedster at first base during the next at-bat, a Sandy Leon strikeout.

“I felt relieved after I got him out,” Perez said, “because it was a big situation and I knew that he was stealing.”

Perez appeared to be tiring when he issued consecutive two-out walks to Dustin Pedroia and Brock Holt. But with Masset and Eveland warming up in the bullpen, Perez took care of things himself by getting slugger Hanley Ramirez to ground into a force at third base.