SAN FRANCISCO -- Randy Johnson looked so awkward on the mound early in his career, that shaggy hair dangling down his neck as he fired a blazing fastball in every direction but the strike zone.

Now, after 22 major league seasons, The Big Unit is walking away from baseball as one of the game's greatest pitchers.

The 6-foot-10 Johnson announced his retirement on a conference call Tuesday, a decision that had been expected from the overpowering left-hander who reached 300 wins last June.

"I really wanted to go out on my terms," Johnson said. "I just feel like there's not a lot more for me to do in this game. I just think it's a natural progression when you play this long. Eventually you have to say it's time."

A five-time Cy Young Award winner, the 46-year-old Johnson accomplished just about everything in his remarkable career that a player hopes for in baseball.

He owns a World Series ring and co-MVP honors, and was a 10-time All-Star. He threw two no-hitters, including a perfect game, and ranks second on the career strikeout list.

Johnson finishes with a record of 303-166 and 4,875 strikeouts in 4,135 1/3 innings for Montreal, Seattle, Houston, Arizona, the New York Yankees and San Francisco. His strikeouts are the most by a left-hander and second to Nolan Ryan's 5,714.

"It's all been a bit of a whirlwind. I never really got caught up in what I did," Johnson said. "I never really dwelled on my achievements. They're nice. Maybe now I'll be able to reflect on them."

Johnson overcame several injuries to keep pitching effectively into his mid-40s. He said before last season ended that he looked forward to going home to Arizona and spending time with his family before making a decision about his future.