Gonzalez was getting Boston out, retiring 12 of the first 13 hitters he faced.
"His curveball was late and he was throwing it for a strike," Red Sox second baseman Dustin Pedroia said. "His fastball was really good, too, 95 [mph] with movement. He's got great stuff. Both of those last two guys [Stephen Strasburg and Gonzalez] we faced are No. 1's. So we've got to find ways to have better at-bats."
Gonzalez felt he could take a deep breath and relax, because he didn't have to hit in the AL park.
"I wouldn't say it was weird [pitching in an American League park]," Gonzalez said. "It was good to be catching my breath once in a while to sit on that bench, take a deep breath. I didn't have to worry about hitting, just try to go out there and worry how to pitch. So you learn from it, and it was fun, especially in Fenway. It's such a beautiful ballpark and great fans. All you can do is enjoy the moment."
Gonzalez was never in any real danger until the seventh inning. It was one out when manager Davey Johnson took Gonzalez out of the game in favor of Craig Stammen. Johnson wouldn't allow Gonzalez to complete the inning because he was rushing to throw his pitches and "was getting a little wild" on the mound, according to the skipper.
"I didn't have that good feeling today in this ballpark," Johnson said, talking about why he took Gonzalez out of the game.
Gonzalez walked Will Middlebrooks and allowed a single to Mike Aviles to put runners on first and third.
"I know I left myself open to be second-guessed by not letting Gio work his way out of it. ... Of course I bring a guy in who is wilder than him," Johnson said. "We have a four-run lead, and Gio walks the first hitter. Then he gets behind on the next one and he gives up the base hit. He was getting in that rush mode."
Stammen came in and walked Ryan Sweeney to load the bases. Left-hander Mike Gonzalez then entered the game to face Jarrod Saltalamacchia, who singled off the Green Monster, scoring Middlebrooks and Aviles to make it a 4-2 game. Both runs were charged to Gonzalez.
After missing a year because of Tommy John surgery, right-hander Daisuke Matsuzaka made his first start of the season for the Red Sox. He lasted five innings, allowing four runs on five hits and a walk while striking out eight.
"We saw a little bit of everything," Nationals first baseman Adam LaRoche said. "He has some really good offspeed [pitches]. He is another guy with a deceptive windup. It's something you are not used to seeing, when a guy has a big pause. We got to him just enough."
Washington scored its first run in the second inning, when LaRoche hit his 10th home run of the season over the right-field wall.
Two innings later, the Nationals added three more runs against Matsuzaka. Ian Desmond highlighted the scoring with a two-run single.
The Nationals, now 34-23 this season, won their 13th series and look to sweep the Red Sox on Sunday. Washington has had 10 chances to sweep a series this season, but they've only been successful once.
"It's staying with the game plan, getting a few runs, sticking with what we have been doing and not try to do too much," LaRoche said. "When we get a few runs sometimes, we may get a little bit out of our rhythm up there."