TUCSON, Ariz. -- It was just the first of many steps, but Randy Johnson can already feel a difference.

Johnson threw off a mound on Friday for the first time since having back surgery in October. The Diamondbacks left-hander threw 25 pitches -- all fastballs -- out of both the stretch and the windup. He also did some agility drills.

"I'm feeling a lot better than I did the last time I picked up the ball, let's put it that way," Johnson said, referring to a Yankees playoff loss to the Tigers in last year's American League Divison Series.

"There's obviously room for improvement, but for the first time I think things went as good as could be expected," he said. "I felt like I was pretty free and easy, and according to everybody that was watching me I was free and easy and the ball was coming out of my hands pretty good."

The session, which was closed to fans and the media, was held in the morning just before the rest of the squad headed across the street to its practice fields.

"Everything went real well," Arizona manager Bob Melvin said. "Couldn't have gone better. Location was good. Really for the first day, health was the only thing we were worried about, but boy, his mechanics looked good and the ball had some life to it."

Johnson, who was reacquired by the D-backs on Jan. 9, said he felt the natural stiffness in his back that comes from throwing the first time in the spring.

Saturday will be an off-day for Johnson, and he'll play catch on Sunday before throwing another bullpen session on Monday.

"We have no timetable with him," Melvin said. "We're not forecasting anything out. That particular day affects how we do things the next time."

"And then, as things progressively get better, I'll do more," Johnson said. "No timetable on anything else other than just progressively getting better and throwing and then everything will take care of itself."

Chris Snyder caught Johnson's session and was impressed with what he saw.

"It was real easy, just effortless," Snyder said. "The ball was coming out of his hand good. He was getting his whole body into it, using his legs quite a bit, wasn't favoring anything, arm slot was good. For the first time out, it was good to see."

Johnson has said that the back bothered him tremendously during the 2006 season, but he pitched through pain en route to winning 17 games.

The D-backs have all but ruled out Johnson being ready when the regular season begins on April 2 in Colorado, but he could be ready to join the rotation sometime after the team's season-opening seven-game road trip.

"I feel if everything was to continue progressing, I'm only really about two weeks behind or thereabouts," he said. "I'm just saying that because these guys have already thrown off the mound three or four times. I felt very pleased, and I think I'm heading in the right direction so I'm very happy about that."