TUCSON, Ariz. -- Randy Johnson wasn't sure what all the fuss was about.

After all, the left-hander, who is coming off his second back surgery in as many years, had thrown three bullpen sessions prior to reporting to camp, so to him his 27-pitch session was more of the same.

But anytime Johnson takes the mound, it's cause for news around D-backs camp.

"Just keep doing what I've been doing, continue to make progress," Johnson said. "The most important thing for me right now is to get on the mound. I did that three times before I got here, so you'll have to ask [pitching coach] Bryan Price and [manager Bob Melvin] what they thought because that was the first time they saw me pitch since the last game against the Dodgers."

That Dodgers game on June 28 was the final one for Johnson before he was forced to go on the disabled list, and he allowed four runs on six hits over three innings.

As for what Melvin and Price thought Sunday, well, consider them impressed.

"First pitch, he's throwing bullets," Melvin said. "Location unbelievable. He's ahead of the game. He's a competitor whether it's throwing a bullpen or pitching in a game. He seemed like he had a little edge when he went out there today so I kind of stayed away and watched and once again marveled at what he had to offer today."

Johnson will play catch over the next three days and continue with his strengthening work. His next bullpen session is scheduled for Thursday. The key for Johnson now is not to overdo it on the mound because he's feeling good.

"In my situation we have to be careful," he said. "At this point right now where I'm at with my health, I don't feel anything while I'm actually doing my side session. There's only so much you can do to simulate those kind of things. Until you get on the mound, you don't know. I'll be careful as far as how many we add and how much I actually throw off the mound."

Taking a look: Trot Nixon worked out for the D-backs at the Kino Sports Complex on Sunday.

Arizona is still looking at the possibility of adding a backup first baseman in case Chad Tracy is not fully recovered from microfracture surgery on his right knee. Tracy is set to try running for the first time on Feb. 24.

"Obviously Tracy is coming along very well," D-backs GM Josh Byrnes said. "Trot offered to come out and work out for us so we said sure. He took some ground balls at first, which is something he worked on this winter. He looked good. It was a good workout. We'll probably know more in a week or so depending on how Tracy does running. We still may end up doing nothing. We'll see."

If Nixon is not signed, the D-backs would likely turn to Robby Hammock to fill in if Tracy were not ready by Opening Day.

Nixon hit .251 with three homers in 307 at-bats for the Indians last year.

New kid on the block: Pitcher Dan Haren, who was acquired in an eight-player deal from the A's in December, has been a target of the media since he reported to camp.

"Most interviews I've ever had," he said. "It's kind of like the All-Star Game. I don't think I'm this popular."

Dealing: Jailen Peguero caught Melvin's eye during his throwing session.

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The right-hander appeared in 18 games as a rookie last year and was 1-0 with a 9.20 ERA. Peguero has an uphill climb to make the roster this year given the depth in the bullpen, but could be one of the first relievers called up from Triple-A Tucson if he pitches well there.

"Peguero threw the ball real well," Melvin said. "In fact, I saw him in the Caribbean Series come in late in some games and get some big outs. He's worked on his sinker; it looks like he keeps the ball down a little more. He's always had the real good slider."

Youngsters Barry Enright, Jarrod Parker and Max Scherzer also received praise from Melvin.

More delays: Juan Gutierrez may not be in camp until Wednesday due to visa problems, while the club is still uncertain when reliever Tony Pena will be able to get his visa issues worked out.

In due time: Johnson hasn't gone through pitchers' fielding practice and the club will limit how much he does later this spring as a way of protecting his back.

"Well, I was never going to win a Gold Glove," Johnson said with a smile.

Don't count on it: Left-handed specialist Doug Slaten probably won't throw off a mound for another week or two as he recovers from microfracture surgery, but Sunday he threw from a few feet in front of the mound during a bullpen session.

"I'm thinking about asking if I can do that in games during the season," Slaten joked.

Monday: The team will once again work out over at the Kino Sports Complex beginning around 9:30 a.m. MT on Monday. The mounds that the pitchers throw off are in an area that the public is not allowed into, but fans can watch pitchers' fielding practice on the main diamonds.