Daniel Murphy homered and had five RBI in the Nationals’ win over the Cardinals. (Jonathan Newton/The Washington Post)

Manager Dusty Baker knows which eight names he’ll write into his lineup card almost every day when his Washington Nationals are fully healthy this season. The starting eight isn’t up for debate. The question is where he’ll slot some of the names. The configuration, Baker has insisted since the Nationals reported to spring training in mid-February, will depend on a few variables. Who is the starting pitcher for the opponent? How many left-handed relievers does that team employ? Who is hot? And so on.

But Baker puts pen to paper with two comforting certainties: Bryce Harper, the 2015 National League MVP, bats third, and Daniel Murphy, the 2016 NL MVP runner-up, bats behind him. That is not up for debate. The rest of the lineup works around that left-handed one-two punch because it is as formidable as any, which the St. Louis Cardinals discovered Tuesday night in the Nationals’ 8-3 win at Nationals Park.

Cardinals starter Lance Lynn walked Harper three times and Murphy punished Lynn twice, knocking in two runs on both occasions. The first instance was a two-run single in the third inning, which extended Murphy’s hitting streak to eight games in the eighth game of the season. The second was a two-run home run into the second deck in the fifth, which was Lynn’s final inning of work.

Murphy added a double in the seventh inning and another one in the eighth to plate Harper, who had doubled. Murphy finished 4 for 5 with five RBI, seemingly putting the barrel on any pitch he pleased. The hits and RBI tied career highs. It was the second baseman’s sixth multi-hit game of the season, and he leads baseball in hits with 17. The Nationals worried Murphy had accumulated rust during an unusually inactive spring training and expected some regression from 2016 regardless. Neither has been evident. Murphy, a sabermetric evangelist, continues to defy expectations and hit and hit and hit.

“He’s talking about the craziest stuff I’ve ever heard of before,” Nationals left fielder Jayson Werth said. “I try not to listen to him, but it’s working for him. He really has a good plan. He knows what he’s doing. If I tried to do that I might never get a hit.”

Harper, appearing to be in 2015 form again, was a worthy partner. His three walks to start his night extended his streak of reaching base to nine plate appearances, which tied a career high. He ended up 1 for 2 with the three walks, a double and two runs scored as the Nationals (5-3) beat the Cardinals (2-6) for the second straight night to begin their three-game series.

“They can be as good as there is in baseball,” Baker said of the Harper-Murphy duo. “They both walk, they both hit left-handers, both hit right-handers. So I’d, like, leave my 3-4 alone and kind of work around that. I’ll just try to find a way to maximize the rest of the guys in the lineup and have some balance up and down the lineup.”

The offensive effort, which also received solo home runs from Matt Wieters and Werth, was plenty in support of Gio Gonzalez. The left-hander required 103 pitches to log seven innings. He yielded two runs (one earned) on six hits. He struck out six and walked none. He has a 0.69 ERA in 13 innings.

“He did an outstanding job,” Baker said.

The night’s only negative development was Stephen Drew’s exit. The utility infielder, who was filling in for Anthony Rendon at third base, hurt his right hamstring running out a groundball in the fifth inning and Rendon replaced him in the sixth. The Nationals didn’t announce any developments after the game, but Baker implied Drew could miss some time.

Gonzalez surrendered a run in the first inning after Dexter Fowler led off with a double, advanced to third base when first baseman Ryan Zimmerman bobbled a transfer on a popout in shallow right field, and scored on Yadier Molina’s sacrifice fly. But Gonzalez threw just 12 pitches in the frame. The next two weren’t as snappy. He yielded two base runners in each inning and tallied 40 pitches between the two. But he dodged damage in both.

The Nationals, meanwhile, continued their very recent trend of hitting with runners in scoring position when Murphy snuck a grounder through the Cardinals’ infield with the bases loaded in the third inning. Two runs — both unearned because of shortstop Aledmys Diaz’s error earlier in the inning — scored on the hit. It was the Nationals’ first hit of the game, and it gave them a 2-1 lead.

“Is it really surprising you?” Gonzalez quipped. “Murph is unreal. Right now, the guy’s a human torch. Can’t touch him. He’s just on fire. He’s just hitting the ball, seeing it big, almost looks like they’re throwing beach balls and watermelons at him.”

Cardinals right fielder Randal Grichuk tallied the first earned run off Gonzalez with a first-pitch home run to tie game at 2 in the fourth inning, but the deadlock was temporary because Werth and Wieters responded with solo home runs of their own in the bottom of the frame. It was the 37-year-old Werth’s third home run of the season and 102nd as a National. It was Wieters’s first of the season and first as a National.

Gonzalez sailed from there. He retired the final 11 batters he faced after Jose Martinez legged out an infield single in the fourth inning.

Joe Blanton relieved Gonzalez and surrendered a solo home run to Diaz in the eighth, but, fittingly, Harper and Murphy retorted with their back-to-back doubles to complete a dominant night for the sturdiest slice of the Nationals’ lineup.

“Murph’s really carrying us right now. Bryce, too,” Werth said. “Those guys are fun to watch.”