PHOENIX -- A.J. Puk did not come to Spring Training with a realistic chance to make the A's rotation right away, and that's probably still true.
But he sure is making things uncomfortable for the A's -- in a good way.
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 The left-handed Puk, the A's top prospect and one of the highest-regarded prospects in baseball, has yet to allow an earned run this spring. He left his most recent lasting impression on Friday, when he shut out the Brewers for three innings, yielding three hits, two walks and two strikeouts in a 2-0 A's win.
Comparatively speaking, it wasn't as smooth as his first two appearances. He was slated to throw four frames, but a higher pitch count ended this one early. His limit was 60, and he was around 55 at the end of the third.
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That didn't take away from the cumulative body of work.
"Using all four of his pitches, he keeps you off balance," manager Bob Melvin said. "I don't know what the [velocities] were on him today -- didn't look from the side as hard as maybe the last time out, but he's got enough to keep you off balance. He pitched well again."
In Spring Training, too much can be made at times of early performances. Exhibition games feature dozens of players, many of whom will not make their team's final roster.
But, when a prospect pitches impressively against a lineup filled with projected starters -- and, in some cases, All-Stars -- it's apropos to make modest judgements.
Puk faced a Brewers lineup consisting of their big offseason acquisition, Christian Yelich, who grounded out twice. Another Milwaukee regular, Travis Shaw, grounded out and walked. Domingo Santana struck out twice.

Ryan Braun, who perhaps ironically is still recovering from a bad bout of the flu, was one of the few projected Brewers regulars to have more than one good at-bat. Braun walked in the first and singled in the third.
"I thought I threw my changeup really well today and I finally threw one good slider -- my last pitch [to Santana]," Puk said. "Overall, I didn't do a very good job with two outs. I threw a lot of extra pitches with two outs trying to get the third out, but overall I felt pretty good."
Puk, who has not pitched higher than Double-A, is performing better than anyone else in A's camp, but is more than likely ticketed for Triple-A to start the season. This is somewhat attributed to teams having to wait a couple of weeks into the season to push a player's free agency clock back a year -- a loophole that is frustrating to fans, but sound business maneuvering for clubs.
Still, while many of Puk's pitching contemporaries have already been sent to Minor League camp or are headed there soon, the lefty has found a little staying power in big league camp. That's what a 0.00 ERA will do for a kid.
"We'll continue to give him starts here, and if he performs well, he'll be later and later in camp," Melvin said.
Camp battles
Veteran righty Santiago Casilla threw a scoreless seventh inning, striking out two, in the A's win over the Brewers. Prior to that outing, Casilla had allowed at least one run in each of his four appearances, including a five-run performance over two-thirds of an inning on Monday versus the White Sox.
Injury update
Camp opened with a lot of promise for outfielder/third baseman Renato Nunez, who was expected to compete for one of the A's final roster spots.
Instead, he's spent most of the exhibition season -- all but two games -- nursing a left hamstring ailment. With time running out to properly prepare for the regular season, each day that Nunez is not able to play is another day closer to him not being ready for Opening Day.
This leaves the A's in a bit of a pickle. Nunez is out of options, so if he doesn't make the team, he'll have to either go through waivers or open the year on the disabled list, which would buy the A's some time.
This wasn't the kind of decision-making process the A's had in mind as Spring Training enters its final weeks.

"This is a guy that is on a bubble, out of options and a guy we have to make a decision on," Melvin said. "Inwardly, I'm sure he's frustrated, but wants to put on a good face. He's rehabbing hard, trying to get back."