Randy Johnson, who will oppose Felix Hernandez tonight in the most wildly anticipated game yet by the 19-year-old Mariners savant, was never a phenom in the traditional sense.

His brilliance was painstakingly slow to develop. He wasn't dropped upon the baseball world, fully formed, as Felix seems to have been. With Johnson, a gangly mess of mechanics in his early days, it was always two steps forward, one step back, until he finally took the giant leap to the land of Cy in his early 30s.

At 19, it's unlikely even Johnson could dream of his future status as the dominating Big Unit, the most intimidating pitcher in the game and a probable first-ballot Hall of Famer, now winding down his career with the Yankees.

"I was just trying to get to class on time when I was 19," Johnson said with a smile on Monday, adding jokingly that his success rate was about 70-30.

It was 1983, and Johnson was a freshman at USC, attending on a joint baseball/basketball scholarship out of Livermore (Calif.) High School. He dropped the basketball portion without playing a game for the Trojans, and appeared in 15 games that frosh year for legendary USC baseball coach Rod Dedeaux.

"He was ambitious, just learning how to get all his muscles coordinating," said Dedeaux, who at age 92 still shows up for work every day at the transportation company he owns in Southern California.

"He was all arms and legs. One thing we all saw in him and admired was his desire, and it proved out. He broke in well as a freshman, and that's not always easy to do when you're two feet taller than everyone else."

At age 19, Johnson went 5-0 with a 5.17 earned-run average for USC. The man who would later strike out 20 in a major-league game and 372 in a season fanned 34 in 47 innings, walking 32.

By the time Johnson left, those numbers had improved — he had 99 strikeouts and 104 walks his final year — but Johnson still didn't have pitching statistics as good as teammate Mark McGwire.

"Every once in a while, he'd let go some good pitches where he put everything together, and you could see it developing," Dedeaux said. "You'd say, 'Wow!' We always told him, 'If you can do it once, you can do it again.' You could see him coming all the way."

Now he is nearly gone, trying to recapture his dominance just in time for the Yankees' stretch drive. On Sept. 10, Johnson will turn 42. The year that Hernandez was born, 1986, Johnson was in his first full professional season, pitching low A ball in West Palm Beach. That was 258 victories, five Cy Youngs and one perfect game ago.

However, this has been his most maddening season since 1998, when the Mariners traded him to Houston and watched him transform into the unbeatable Unit that had been missing all season in Seattle.

"I'm making some adjustments," he said. "There have been some good games I've pitched, but probably more games I haven't really been happy with. I'm entitled to have a bad year, I guess. I'm not saying it's going to be a bad year. I still have seven starts left. And hopefully beyond."

By the standards of what the Yankees expected when they acquired him from Arizona last winter — a dominating No.1 ace — it has been a bad year: 12 wins, eight losses, a 4.20 ERA.

Not surprisingly, given his well-earned reputation as a perfectionist and an intense hot-head, Johnson has not been the happiest of campers.

"Anything less than a win has always been unacceptable to me," he said. "I've won games and given up two runs and I'm upset about giving up two runs. There's been a lot of games I've given up five to seven runs this year. So you can imagine how upset I am walking off after giving up six or seven."

But Johnson had an encouraging start his last time out against Kansas City (eight innings, four hits, six strikeouts, one run, and a 96 mph fastball), which the Yankees hope is a sign that he will deliver what they desperately need down the stretch to catch Boston.

"He's always been our guy," Jason Giambi said. "We're going to go as far as he takes us, no doubt about it."

Johnson says he doesn't know much about Felix, had barely heard of him until Mariners announcer Dave Niehaus filled him in. This showdown may have captivated Seattle, and energized Hernandez, but Johnson makes it clear that he's not going to play along.

"I'm not getting worked up about it," he said. "I've faced Nolan Ryan, Roger Clemens before, guys like that. I don't worry too much about who I'm throwing against. I don't have to hit."

Said Yankees manager Joe Torre: "Randy's more into challenging himself than something else has to stimulate him."

Nor does Johnson expect to carry any emotional baggage from the fact that this will be his first game at Safeco Field since July 20, 1999, when he pitched an eight-hit shutout for the Diamondbacks.

"There's no sentimental feelings now," he said.

His reception back in '99 — at the sixth game ever played at Safeco Field — was wildly positive, marked by a series of standing ovations.

"That was very nice. I gave it everything I got here," he said with a shrug. "The fans saw the raw Randy Johnson, and toward the end, they saw what Arizona saw the majority of the time I was there. Seattle saw kind of two sides of me — the person that was getting there, and the person that eventually got there."

Larry Stone: 206-464-3146 or lstone@seattletimes.com