Bryce Harper took exception to an inside pitch from the Cubs’ Lendy Castillo. (AP)

WASHINGTON—Nationals manager Davey Johnson figures the Cubs were ticked off because Jayson Werth swung at a 3-0 pitch in the fifth inning. Just to be clear, Johnson wasn’t apologizing. Adam LaRoche added to his home run tear with a two-run shot and Washington beat the Cubs 9-2 in a fight-filled game Thursday night to finish a lopsided four-game sweep.

“If they get mad at my guys in the fifth inning swinging 3-0 or running, they better get used to it,” Johnson said.

The trouble started with a testy exchange between Cubs bench coach Jamie Quirk and Nationals third base coach Bo Porter in the fifth. Quirk shouted from the dugout toward third base and Porter walked over to the railing, jawing and pointing his finger.

The benches and bullpens emptied, but there was no pushing or shoving. Quirk was ejected before play resumed.

“It was the bench coach’s frustration in us handing it to him for a couple days,” Johnson said. “If they want to quit competing and forfeit, then fine. But we’re going to keep competing.”

In the sixth, Cubs reliever Lendy Castillo threw his first pitch of the inning near Bryce Harper’s legs and the ball that sailed all the way to the backstop.

“Castillo’s a Rule 5 kid who’s thrown a lot of them pitches today,” Manager Dale Sveum said. “There was no intention to hit Bryce Harper or anything because of what happened.”

Harper made a move toward the mound and was quickly intercepted by catcher Steve Clevenger.Both teams spilled onto the field again, and this time things got a little nasty. Players pushed and shoved each other in the infield and Clevenger took an open-handed swipe at Washington shortstop Ian Desmond, who accidentally knocked down first base umpire Bill Miller while backing away.

“I’m just trying to check off everything on my list this whole year,” Harper said. “I’ve gotten thrown at, gotten hit, stole home.”

Clevenger, Cubs right-hander Manny Corpas and Nationals lefty Michael Gonzalez were ejected — though neither pitcher was in the game. Order was finally restored and Washington went on to its fifth straight victory and eighth in nine games.

“All that stuff that happened, that was instigated by Quirk screaming out at Porter,” plate umpire Jerry Layne said. “And the obscenities that he screamed out I just felt was inappropriate, and that’s what caused everything. The reason he was ejected was he was the cause.”

Porter declined to get into specifics. But he did have something to say about the dust-up.

“When I was younger, I did Gold Glove boxing,” he said. “My trainer would always tell me before the bell rang, `Just in case you didn’t know, when this bell rings, that guy over there, he’s going to hit back.”‘

The Nationals (85-52), who have the best record in the majors, remained 7½ games ahead of second-place Atlanta in the NL East. The Cubs (51-86) have lost 17 of their last 18 road games and six in a row overall. They were outscored 31-9 in the series.

“It’s probably one of the biggest butt-whippings I’ve ever gotten in my career, as a coach or player,” Sveum said. “I don’t remember getting manhandled that bad in any kind of series I’ve been a part of.”

Kurt Suzuki hit a three-run homer to help back Jordan Zimmermann (10-8), who struck out nine in seven innings. LaRoche hit his seventh home run in his last six games. Washington tied a franchise record in each of the previous two games with six home runs. Harper set the tone for the Nationals in the first inning Thursday, turning an apparent double into a triple and then sliding headfirst to score from third on a groundout.

“He might be the only guy that can do that,” Johnson said.

Zimmermann, who allowed two earned runs and five hits, joined Gio Gonzalez and Stephen Strasburg as Washington pitchers with double-digit wins. Edwin Jackson and Ross Detwiler each have nine. Harper also scored in the fourth inning, when he hit an infield single and came around from second on Ryan Zimmerman’s two-out single.Justin Germano (2-6) allowed seven hits and seven runs, six earned, in four innings — his shortest start of the season.Anthony Rizzo homered in the first on a 3-0 pitch to give the Cubs their first lead of the series. The Cubs added another run in the second on triples by Starlin Castro and Darwin Barney.

“I respect every one of those guys in the other clubhouse. But again, I think that sometimes they need to learn how to play the game a little better,” Miguel Gonzalez said. “There was nothing wrong with how we’re playing ball.”

NOTES—Strasburg (15-6, 2.94 ERA) is scheduled to make his final home start of the season Friday against Miami rookie Jacob Turner (0-2, 6.55). Johnson doesn’t expect Strasburg will change his approach. “He’s all in,” Johnson said. “Every time he goes out, he’s committed to being the best he can be. He probably puts that standard higher than I’d like him to.” ….Johnson said LHP Sean Burnett, who has been bothered by an inflamed nerve in his elbow, will play catch Saturday….Zimmerman extended his hitting streak to 11 games…..Travis Wood (4-11, 4.64) will pitch for the Cubs on Friday against Pittsburgh RHP A.J. Burnett (15-5, 3.63).