CINCINNATI – One starter couldn’t throw strikes. The other was blowing away hitters with one of the best arsenals in baseball. Together, it made for a bad combination for the Nationals.

With Mitchell Parker issuing five walks in his second consecutive shaky outing, and with Hunter Greene racking up 12 strikeouts in six innings against a helpless lineup, the Nats stood no chance tonight in their series opener at Great American Ball Park, falling 6-1 to the Reds in a game that never really felt within reach.

Parker dug his team into an early hole and didn’t make it to the fifth inning for the first time this season. Greene took full advantage of the cushion his teammates provided him and went right after the Nationals, who could only muster a ton of foul balls against the young Cincinnati hurler on a frustrating night that also included a lengthy rain delay.

“He’s their ace,” manager Davey Martinez said. “He was good tonight.”

Command hadn’t been a problem for Parker through the season’s first month. He issued only 11 walks through his first 32 innings, and not surprisingly boasted a 1.39 ERA at the time.

But something changed for the left-hander in his last outing, when he issued four free passes to the Mets in the top of the first and five total across five innings. And that trend carried right over into tonight’s game against the Reds.

After being forced to wait out a 1-hour, 51-minute rain delay, Parker took the mound and immediately got himself in trouble, issuing back-to-back walks to Matt McLain (with one of his pitches sailing to the backstop) and Elly De La Cruz in the bottom of the first. Both proceeded to score on Santiago Espinal’s two-out double to left-center.

Parker issued another walk to Tyler Stephenson to open the second inning, and sure enough, Stephenson later scored on a fielder’s choice to make it 3-0. And just for good measure, he walked Espinal in the bottom of the third, then watched as he and Spencer Steer (who reached on an infield single) both scored on Stephenson’s two-run double to make it 5-0 and ruin any chance of Parker salvaging this start.

“My bullpens between the outings and before the outing are good,” he said. “And then it’s like I lose focus when it matters.”

That made nine walks issued by Parker over a stretch of eight innings, seven of them eventually coming around to score, as they so often seem to do.

“One thousand percent, this year I’ve beat myself more than I’ve been beat,” he said. “It’s frustrating, because it’s a simple fix, but not an easy one. I’m beating myself.”

Parker wound up lasting only four innings tonight, the shortest start by a member of the Nationals rotation this season other than Brad Lord (who had a restricted workload while building his arm up after opening the year in the bullpen).

“I think he’s just a little quick,” Martinez said. “We’ve got to get him to slow down a little bit, stay in his legs, and he’ll be OK. When he did get on top of the ball, everything came out pretty good. But when you fall behind hitters and start walking guys, you put yourself in a bad situation.”

The Nationals needed way more from Parker tonight to have any chance, because the challenge they faced at the plate was as difficult as any they’ve faced in a while.

Greene has long been touted as one of baseball’s most exciting young arms, and now in his fourth major league season he’s putting it all together in spectacular fashion. The flamethrowing right-hander had the Nats eating out of his pocket all night with his triple-digit fastball, sharp-breaking slider and bowling ball splitter.

Through four innings, only one batter managed to hit the ball out of the infield. For a three-inning stretch, nobody hit the ball past the pitcher’s mound.

Josh Bell finally connected in the top of the fifth, sending a 99 mph fastball on a beeline straight into the right field bleachers for his fifth homer of the season. That was the Nationals’ second and last hit of the night off Greene.

“From what I saw, he was making very good pitches,” said Bell, who tweaked his groin running out a grounder in the seventh and was pinch-hit for in the ninth. “And he didn’t really miss in the heart of the plate very often. Sometimes, you’ve got to tip your cap.”

They did make him work, fouling off a staggering 40 of his 114 total pitches, with only eight balls put into play in six innings. He punctuated a 10-pitch battle with Keibert Ruiz with his 12th strikeout, walking off the mound to an ovation as his night came to an end.

“Hey, we tried to compete with him,” Martinez said. “But his stuff was good today.”