MIAMI -- Even among strikeout pitchers, Randy Johnson is the fastest ever.
Johnson reached 300 strikeouts in record time, notching nine in seven innings Thursday to help the streaking Diamondbacks beat the Marlins 12-2.
Johnson (14-8) achieved the milestone in his 29th start. The previous best was Pedro Martinez, who reached 300 in 31 starts in 1997.
"It's a special achievement," Johnson said. "My primary goal is to put us in a position to win, but anything that comes with that is great."
Damian Miller hit a grand slam to cap Arizona's team-record eight-run ninth. Matt Williams drove in four runs with two singles, a double and a sacrifice fly. Tony Womack had two hits and a walk, two stolen bases and three runs scored.
The NL West-leading Diamondbacks extended their winning streak to six and completed a three-game sweep of Florida, which has lost six in a row.
Johnson reached 300 strikeouts with his eighth of the game against Kevin Millar to end the fifth.
"If I had to face Randy Johnson every night, I probably wouldn't be here," said Millar, who struck out in all three of his at-bats. "You can have your A-game, and he can make it a D-game real quick. You feel real good at the plate, and you look up and you've struck out three times."
Johnson, who also achieved the strikeout milestone in 1993 and 1998, joins Nolan Ryan and Sandy Koufax as the only pitchers to reach the 300 mark three times. Ryan had a record six 300 seasons.
"I don't know if everybody grasps the type of achievement that is," Diamondbacks manager Buck Showalter said. "We're all lucky to be here to see it. Randy is having as good a year as he's ever had, and he's had a lot of good ones."
On a sunny, 88-degree afternoon, Johnson left the game with a 4-1 lead and 301 strikeouts after throwing 103 pitches. He allowed six hits.
Johnson, who has lost several low-scoring games, said this has been his best year. The 35-year-old left-hander likely has seven starts remaining, and he needs 83 strikeouts to break Ryan's one-season record of 383 set in 1973.