CINCINNATI -- Stephen Strasburg traditionally hasn't fared well in hot weather, so much so that trainers have developed a hydration process for the Washington Nationals right-hander.

On Monday afternoon in Cincinnati, the game-time temperature was 85, but Strasburg managed to keep his cool through seven innings.

Bryce Harper hit a three-run home run and Ryan Zimmerman and Brian Goodwin added solo shots to back Strasburg and help the Nationals complete a four-game sweep of the Reds with a 6-1 victory at Great American Ball Park.

A five-run first inning provided plenty of run support for Strasburg (10-3), who gave up only one run on four hits. He struck out 11 for his sixth 10-plus strikeout game of the season and 35th of his career.

Throughout Monday's game, trainers provided Strasburg with continual fluids on the bench. The special mixture appears to be working.

"The training staff really kind of put their heads together and got a good (hydration) system for me," Strasburg said. "It kind of takes the guesswork out of it and I can just focus on the game. It's a pretty good setup."

Zimmerman's home run moved him past Vladimir Guerrero for first place on the all-time Nationals/Expos franchise home run list with 235, and manager Dusty Baker presented Zimmerman with the scorecard from Monday's game.

"It's special to be in one place your entire career," Zimmerman said. "You can't do stuff like this if you're not in the same place for a long time. So, I feel very lucky to have spent my entire career here, honored to have hit more home runs than any Expo or National. It's cool."

The Nationals (56-36) outscored the Reds 35-12 and hit 13 home runs in the series to extend their winning streak to five.

"We've been flirting with sweeps quite a few times but just don't complete that last game," Baker said. "We're just trying to win as many games as we can."

Eugenio Suarez hit his 13th home run for Cincinnati (39-53), which was swept in a four-game series by the Nationals for the first time at Great American Ball Park.

Monday's game could prove costly for the Reds, who lifted starter Scott Feldman after an inning due to right knee soreness. It's something Feldman has pitched through at times this season, but the latest occurrence could land Cincinnati's most consistent starter on the disabled list.

"He's had it on and off all season," Reds manager Bryan Price said. "He's been getting treatment and he's been effective. Today, he felt it coming out of the bullpen, but that's happened before and felt like he could pitch with it. I think he's going to need a stint on the disabled list. It would be unfair for Scott and for the ballclub to keep sending him out there not knowing how he's going to feel."

It took only 12 pitches in the first inning on Monday from Feldman (7-7) for the Nationals to score four runs.

Goodwin led off with a double, Stephen Drew singled and Harper launched his 23rd home run. On the next pitch from Feldman, Zimmerman hit his 20th homer to set a franchise mark and put the Nationals ahead 4-0.

"We jumped them early," Baker said. "When you're going for a sweep, it kind of deflates the opposing team a little bit. It's like, 'Here they go again.'"

Daniel Murphy walked, later tagged and scored from second when right fielder Scooter Gennett made a diving grab on Matt Wieters' line drive but dropped the ball while taking it out of his glove.

Washington sent nine batters to the plate in the inning scoring five runs on five hits, two homers and a walk.

Asher Wojciechowski took over for Feldman in the second inning and limited the Nationals to only one hit over 4 2/3 innings before Goodwin hit a solo home run with two outs in the sixth. Wojciechowski kept Washington off-balance, recording seven outs on pop flies over his five innings.

Cincinnati's bullpen allowed only one run on six hits over eight innings, but enough damage was done early by the Nationals.

"We know we have a good team and we've put ourselves in a good spot to start the second half," Zimmerman said. "But we've got a ways to go."

NOTES: The Nationals selected the contract of RHP Jacob Turner and transferred RHP Koda Glover to the 60-day disabled list. ... RHP Ryan Madson and LHP Sean Doolittle, acquired by the Nationals on Sunday in a trade with the Oakland A's, are expected to join the team on Tuesday in Anaheim. ... Reds C Devin Mesoraco began a rehab assignment at Triple-A Louisville on Monday. He's been on the DL since July 23 with a left shoulder strain.