WASHINGTON -- The emotions finally flowed for Randy Johnson when the final out was made.

A hug for his son, who was serving as batboy. Hugs for every teammate, plus a really big one for his manager. The game ball presented to his wife as his three daughters beamed with pride. A news conference that lasted a half-hour from a player who usually doesn't have much to say. Someone even spotted a smile.

The Big Unit admits he can come across as surly, and he did his best over the past few weeks to downplay his pursuit of 300 wins. Once he got there -- with a steady, six-inning performance in the San Francisco Giants' 5-1 victory over the Washington Nationals on Thursday -- he was free to express that, yes, it really is a big deal.

"I think it kind of hit me when I walked on the field," Johnson said. "It's a long-range achievement. It's not a one-game or a one-year achievement, it's a career achievement. Who knows how many teammates I've had over my 21 years, but they had a great deal to do with my success. I'm going to think about this for a long time."

Johnson became the 24th pitcher to reach the milestone, and he did it as a mature pitcher, not the overpowering tangle of arms and legs who was all about strikeouts early in his career. He walked two, struck out two, allowed only an unearned run and threw 50 of his 78 pitches for strikes. He faced four batters above the minimum and got shutout relief from his bullpen.

"I get more gratification out of that because of the way I'm doing it now than the way I did it 10 years ago," Johnson said.

It was hardly the ideal setting for a historic moment. The crowd was small and the weather was wet. Some of the few thousand fans who witnessed the feat -- the Nationals have trouble drawing a crowd for anything these days -- chanted "Randy! Randy!" in the bottom of the ninth, and he tipped his hat to them all.

Family and friends from all over flew in for the occasion to see Johnson (5-4) become the first pitcher to get 300 on his first try since Tom Seaver in 1985.

"He's become one of the dinosaurs with the other 23, and he didn't want to make a big deal out of it," Giants manager Bruce Bochy said. "But you could see after the game -- I'm sure he's had his eye on this 300 for a while. He's done an incredible job with keeping his self in shape, pitching at 45 and still throwing the ball the way he's throwing is quite an accomplishment."

Johnson had to leave the game because of what he called a "senior moment" -- his decision to go after a comebacker that he knocked down in the sixth inning. The 6-foot-10 Johnson barehanded the ball while falling forward to throw out the runner and bruised his pitching shoulder on the play. He's not expected to miss his next start.

San Francisco led 2-1 when Johnson departed, but he nearly wound up with a no-decision. The Nationals loaded the bases with two outs in the eighth before Adam Dunn was called out on strikes with a full count on a knee-high fastball from reliever Brian Wilson.

The 45-year-old Johnson is the sixth left-hander to win 300 games and the second-oldest pitcher to reach the milestone. Knuckleballer Phil Niekro was 46 when he won his 300th with the New York Yankees in 1985.

As long as it took to get to 300, the final step required quite a bit of patience. Two off days in the Giants' schedule and a rainout Wednesday night gave him seven days of rest after winning No. 299 last week against Atlanta. In addition, Thursday's game -- the first in a doubleheader -- was delayed 36 minutes by bad weather and was played in a light rain.

Once he finally got on the mound, Johnson had an efficient outing, not flashy. He didn't allow a baserunner until a walk in the fourth inning and didn't give up a hit until Elijah Dukes' broken-bat single up the middle in the fifth.

Johnson then walked Austin Kearns, putting runners on first and second with none out. But second baseman Emmanuel Burriss thwarted a rally with the defensive play of the game. On a one-hopper that hit the mound, Burriss dived to his right to stab the ball backhanded, then flipped it out of his glove to shortstop Edgar Renteria to start a dazzling double play.

The unearned run came on Nick Johnson's double in the sixth, following a throwing error by Renteria.

Randy Johnson got the run support he needed early, when Juan Uribe's RBI grounder and Burriss' RBI single off Jordan Zimmermann (2-3) gave the Giants a 2-0 lead in the second. San Francisco added three runs in the ninth.

After Johnson was pulled, relievers Brandon Medders, Jeremy Affeldt and Wilson took care of the rest, although Wilson's strikeout of Dunn was a borderline call disputed by the Nationals slugger. Wilson also worked the ninth for his 13th save.

Johnson joined Steve Carlton as the only pitchers to win No. 300 against the organization with whom they made their major league debut.

Johnson's first three wins -- exactly 1 percent of his total -- came with the Montreal Expos, long before the franchise moved to Washington. His first victory was Sept. 15, 1988, five days after his 25th birthday, but most people noticed him only because he was the tallest player in the majors.

"We watched history today," Nationals manager Manny Acta said. "He's probably going to be the last guy to ever do this. It was impressive to see. His longevity and everything he's done for the game paid off today."

Game notes

Johnson is the fourth pitcher to win his 300th with the Giants, joining Christy Mathewson in 1912 and Tim Keefe and Mickey Welch, both in 1890. ... Washington OF Josh Willingham remained sidelined with a stomach virus.