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03/26/08 9:02 PM ET

Johnson feels fine in Minors outing

Unfazed by subpar line, Big Unit tinkers with offspeed pitches

TUCSON, Ariz. -- Randy Johnson was part mad scientist Wednesday afternoon and the Minor League fields behind Tucson Electric Park were his laboratory.

Johnson allowed five runs on nine hits over 3 1/3 innings against White Sox Minor Leaguers, but coming off his second back surgery in as many years, Johnson is focused more on his health than his stats.

"Of all the Spring Training starts I've made, I actually physically felt the best today," Johnson said. "The results may not have been there, which is OK because I didn't care about the results. I was giving up base hits, but I was throwing three straight changeups. My opportunity to work on things now is critical because I don't have very many starts left."

And one of the things Johnson is working on is his changeup, a pitch he hardly used in 2007. It's a pitch that the big left-hander is thinking about using as an offspeed pitch instead of his split-finger fastball.

Next time out, look for him to throw more splits as he tries to decide between the two.

"I want to see what's going to be better for me," Johnson said.

Johnson has now appeared in four games this spring. Prior to the Minor League game, he had started March 10 against the Rockies, March 15 against the Angels and March 21 against the Dodgers.

D-backs manager Bob Melvin said Johnson's next start will be April 3, which is Opening Day for Triple-A Tucson.

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"I did work on my endurance," Johnson said. "Throwing 75 pitches was really what I needed to do. Get out there and put myself in situations where I can get a lot of work in. I was able to do that today and feel good about it from a physical standpoint. I worked on a lot of things that I otherwise haven't worked on at all this spring."

Though Melvin didn't say it, it seems likely Johnson would make two Minor League starts before joining the big league rotation sometime in mid-April.

Johnson has not taken batting practice this spring in an effort to take it easy on his back and has done limited pitcher's fielding practice. He did get a chance to work on fundamentals during Wednesday's game when his inside pickoff move caught a runner leaning off second and participated in the rundown.

"That's why I was kind of glad that I put myself in situations where I had to pitch from the stretch and do these things," Johnson said. "Until you actually get between the lines in a game, that's when you know what you have on that given day because you're trying to get someone out and being able to field your position and incorporate all your pitches."

Or in Johnson's case, incorporate a new pitch.

"Just trying to re-invent the wheel," he joked. "I like tinkering with pitches and stuff."

Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.