Johnson paid tribute to all of his teammates throughout his long career at a press conference following the game. He said his accomplishments wouldn't be possible without them, and there's no question the Giants enjoyed helping him.
"It's an amazing feeling," said catcher Bengie Molina. "It's real amazing for us to go through this, and we don't know if there's going to be somebody else with 300 wins, so we might be witnessing history. It means a lot to us, believe me."
Tim Lincecum expressed similar thoughts after the nightcap, when San Francisco (27-25) completed the sweep with a rain-shortened 4-1 victory.
Lincecum was on the team when Barry Bonds broke Hank Aaron's all-time home-run record -- also against the Nationals -- two years ago.
"[I'm] just lucky to be here," Lincecum said. "I've been pretty fortunate to be on this team in two big milestone achievements in people's careers with Barry and [Randy]. To be on a team with those guys when they did that, that's just a privilege for me to be there and witness it."
Giants closer Brian Wilson had a bigger role than most, getting the save that let Johnson (5-4) earn his 300th victory.
But Wilson had a few scary moments. He came on with two outs and two on in the bottom of the eighth, and the Giants clinging to a 2-1 lead.
Wilson pitched carefully to Washington's Ryan Zimmerman and walked him to load the bases. Adam Dunn then ran the count full on Wilson before the closer caught him looking on a very close pitch.
Home-plate umpire Tim Timmons took a moment before calling strike three as Dunn was several feet up the first-base line and immediately began protesting. But that ended the inning and kept Johnson as the pitcher of record.
"If he needed some help out of the bullpen, I was more than happy to come in for him," Wilson said. "It was an honor."
When asked about the 3-2 pitch, Wilson said he had no problems with it.
"[I] liked it," he said with a smile. "It worked out. I pretty much wanted it just about right down the middle. He took it. I can't really speculate on where it was. I just know the ump called it a strike -- very advantageous for us, so I'll take it. [I] didn't want to see a 300th game lost on a walk."
Giants manager Bruce Bochy was glad that Johnson got it done on the first try and didn't have to keep trying and answering questions about it.
Even more, Bochy truly appreciated being part of the moment.
"It was great to be part of history," Bochy said. "They wanted to win this game for him. Randy, I'm sure, eventually will sit back and see what he has accomplished. We don't know if we'll see another one. It's neat to be part of it."