Nationals right-hander Stephen Strasburg throws a warmup pitch as Manager Dusty Baker and pitching coach Mike Maddux watch during the sixth inning against the Reds. Strasburg stayed in the game despite apparent discomfort in his leg but did not finish the inning. (Kirk Irwin/Getty Images)

On a sixth-inning pitch to Brandon Phillips, Stephen Strasburg grimaced and reached for his calf. Washington Nationals Manager Dusty Baker, trainer Paul Lessard and pitching coach Mike Maddux jogged out to check on the right-hander, who threw a practice pitch and stayed in the game.

Moments earlier, Strasburg had come back from a 21-minute rain delay and given up the lead on a two-run homer from Joey Votto. Moments later, after a single by Jay Bruce and with Strasburg’s pitch count at 97, Baker had seen enough and pulled his starter.

“It kind of locked up on me again, but I did everything I could to get through that inning. It just didn’t work out that way,” Strasburg said.

The Nationals rallied to tie in the eighth, but the bullpen couldn’t keep it there in a 6-3 loss, ending a string of 15 consecutive Strasburg starts that resulted in a Nationals win.

The key blow came from Adam Duvall, who blasted a slider from Shawn Kelley into the second deck in left field for his 16th home run, a three-run shot that sealed the outcome.

“Shawn has been lights out all year,” Baker said. “. . . He kind of threw a cement mixer up there that didn’t break to a hot hitter.”

Kelley was running out of the bullpen with two outs in the eighth inning when the rain picked up. Once play resumed after a 64-minute delay, Kelley took the mound and inherited Felipe Rivero’s two runners. The extra time didn’t do Kelley much good.

“Those runners didn’t mean anything to me with two outs. It was getting that hitter,” said Kelley, who has allowed only one other home run. “That was the only job. And if you get him, strikeout, popout, groundout, whatever, you are out of the inning. So I was focused on the hitter and didn’t execute the pitch.”

For the first five innings, the game was a pitchers’ duel. Reds right-hander Dan Straily, the best pitcher on one of the worst staffs in the National League, matched Strasburg save for one mistake — a change-up that Anthony Rendon rocketed to left for a two-run home run in the second inning.

“I feel like I’ve been hitting the ball hard, relatively hard throughout the whole season,” Rendon said. “Balls are starting to go a little further in warmer weather and starting to find some holes in the outfield.”

Strasburg held down the Reds for five innings. He yielded a second-inning home run to Bruce but on a tough pitch, a change-up away that the outfielder flicked to left field for a solo blast.

Washington Nationals pitchers Max Scherzer has nearly 60 dives under his belt and has traveled to Fiji, Mexico and the Caymans. (Max Scherzer)

“This is one of the most homer-friendly ballparks in baseball,” Baker said. “He’s not infallible.”

In the fifth inning, Strasburg fanned Straily for his 1,000th career strikeout, the first pitcher to fan 1,000 in a Nationals uniform. He is the second fastest to reach that milestone in all of baseball, doing so in 855⅓ innings, topped only by Kerry Wood, who accomplished the feat in 853 innings.

“Absolutely, it’s great,” Strasburg said of the milestone. “Great to get the ball, I guess. But it seems like I have a few balls that have pitchers as strikeouts on there.”

The game changed in the sixth inning after the shower blew through. Straily had little issue with the brief interruption. Strasburg stumbled and didn’t look the same. He hydrated his body for the humid day, but the cramping still struck. Baker said the Nationals believe it is not a calf strain and simply cramping.

“It’s no different than getting a cramp anywhere,” said Strasburg, who added his calf felt fine after postgame treatment. “Just sometimes it happens.

“I made some good pitches inside, just wasn’t getting the calls, so it can be a challenge when you try and establish fastball in and they don’t have to honor it,” Strasburg said when asked about his pitch to Votto.

After the mound visit and Bruce’s single, Baker removed Strasburg. He trudged off the field, replaced by Blake Treinen. Danny Espinosa tied the score in the eighth with a solo shot on a 3-0 pitch. It was his fifth home run in nine games. There were more storm clouds to come.

“It’s tough,” Espinosa said. “The rain delays are always tough. It seems like every year we get a lot of rain throughout the season. I feel like it’s something this team is kind of used to.”