If there has been one steadfast, impressive truth three weeks into the Washington Nationals season, it’s that Ross Detwiler, the fifth starter of a rotation expected to be among the game’s strongest, has been the team’s best pitcher, and among the best in baseball. Detwiler fired a career-best 107 pitches — 80 for strikes — over seven innings Wednesday night in a 6-1 win over the Miami Marlins. The offense, sparked byKurt Suzuki and a flu-riddenBryce Harper, who received intravenous fluids before the game, provided enough support for Detwiler’s first win. Last season, Detwiler emerged as a vital piece of the Nationals’ foundation, finally harnessing the talent that prompted the organization to select him with the sixth overall pick in the 2007 draft. The left-hander came into Wednesday’s start averaging 92 mph on his fastball and was hitting 95 mph in the seventh inning. Also of note: He is only 27 years old, with few innings on his arm and under team control through the 2015 season. He closed last season with an outstanding, nerve-wracking start in Game 4 of the National League Division Series, and has picked up where he left in 2012. Detwiler, who has a 2.90 ERA over his past 18 starts, has dominated with his fastball. Against the Marlins, only seven of his pitches were offspeed, one of which was hammered for a double by Placido Polanco. In three starts, only 31 of his 279 pitches have been offspeed. “A well-located fastball is still the hardest pitch to hit in the big leagues,” Ryan Zimmerman said. “Some people forget that sometimes.” Detwiler throws a four-seam fastball and a two-seamer, which Detwiler leaned on as he tired in the later innings. They move differently, and mixing them helped produced five strikeouts and 11 groundballs. Manager Davey Johnson has kept a tight leash on Detwiler, limiting how deep he will throw in a game. In the top of the seventh, Johnson let him hit for himself, his trust growing. “It’s great especially since my spot came up in the order and he let me go up there and strike out again,” Detwiler said. “That was good. But I felt strong at the end. That’s something I’m going to need to do down the road anyway, so it was good to get it out of the way early.” Detwiler’s defense backed him up, save for a miscue by Ian Desmond (his team-leading fifth error) that didn’t lead to any runs. Zimmerman, much maligned over the past five games for a handful of costly errors, made all of his plays, including a slick play on a groundball in the sixth that required him to range to his left, charge, scoop and fire a strike to Adam LaRoche across the diamond. A close play at home was the only blemish on Detwiler’s pitching line. Chris Valaika led off the fifth inning with a double to center. Two batters later, with two outs, Donovan Solano lashed a sinker to right field to Jayson Werth. Werth fielded the ball cleanly and fired a two-hop strike to Suzuki as Valaika tore home. The catcher scooped up the ball, spun to his left and reached to tag Valaika. Suzuki’s glove appeared to nab Valaika on the top of his helmet before Valaika’s right hand tagged home plate. Watching from the other side of the plate, home plate umpire Greg Gibson started to pump his fist to signal an out before stopping and calling Valaika safe. Suzuki hopped to his feet to argue and Johnson emerged from the dugout to do the same. Detwiler, near home plate, put his hands on his head. “I was wondering if he was looking if I didn’t have the ball because I showed him the ball that I had it and he still called him safe,” Suzuki said. “It was a little interesting.” The win also highlighted the Nationals’ depth. Suzuki, who has assumed the role of everyday catcher with Wilson Ramos (hamstring) on the disabled list, provided offense with a solo home run off Marlins starter Ricky Nolasco in the fifth inning. He then legged out a triple to left field to lead off the seventh inning, scoring three batters later. Second basemen Steve Lombardozzi, starting again for Danny Espinosa as he nurses a sore wrist, went 6 for 14 with four RBI this series. While Harper was sick with the flu on Tuesday, Tyler Moore started in his place. On Wednesday, Harper wasn’t going to let the remnants of the flu hold him out of the lineup. Harper was given an IV before the game and threw up in the second inning. “I didn’t feel very good at all,” he said. “I was bent over at home plate multiple times.”