The wide-eyed rookie nervous about making mistakes and trying to sort out all the information coming his way has been replaced by a confident defender determined to own the center-field position.
"He's come a long way," Pettis said. "The one thing I want him to take from all of this is you don't have to think about how you're doing it as much as he does as opposed to just going out and doing it. That's where experience comes in. The more you do something, the less you think about it. He's on his way to becoming that kind of player."
Don't underestimate how important Borbon could be to this team. If he can play solid enough defense in center field, Josh Hamilton can stay in left field, where the wear and tear won't be as great on his body. If Borbon can get on base more, he can use his speed to create more runs and set the table for the top of the lineup.
Borbon got off to a rough start in 2010, losing his job as the leadoff hitter before April was over. He hit just .191 in April but, after moving to the bottom of the order, managed to rebound and hit a little more than .290 the rest of the way. He stole just 15 bases, mainly because he didn't get on base enough.
Borbon said his first full season in the major leagues provided some valuable lessons.
"As a first-year guy, you have some things you have to deal with that you're not used to," Borbon said. "Sometimes you just want to catch your breath. You have to learn how to fight through things and keep your focus and realize that anytime you let down could be the difference in the game."
Borbon admitted that he would sometimes lose focus, in part because he was fatigued.
"It's hot and you have to figure out how best to handle that," Borbon said. "I know my body better and what I have to do to stay focused."
Borbon spent much of 2010 working on his throwing mechanics and taking the most efficient routes to fly balls. Those were two areas of heavy emphasis with Pettis.
"The work that I've put in and the things that I've done have paid off," Borbon said. "When I got out there and went after balls, even three or four years ago, I'd sometime over run them or short them because I wasn't taking the proper route. I'm much better at that now but have way, way more room to grow."
Borbon said a big key to his improvement is using batting practice the right way. He isn't just hanging out in center field while his teammates hit balls. He's practicing his positioning and taking the best angles to balls that are hit.
"There's a big difference running after balls off guys that hit line drives in the big leagues than those in the minors or college," Borbon said. "Sometimes those balls might tail off or hang up, and you can adjust. But these guys get around, and you have to know where you're supposed to be and get there. You have to pay attention and be in the right spot. That's very important in center."
Borbon is 8-for-16 at the plate this spring and is working toward becoming a hitter who can do more than bunt his way on, something Pettis said Borbon can do "whenever he wants to."
Hitting coach Thad Bosley has worked with Borbon on getting a little more power behind his swing in an effort to get more extra-base hits.
"I want to make the most out of my abilities offensively," Borbon said. "That means putting myself in better counts to be able to drive the ball better. It's not only being aggressive at times, but smart about when to swing at first pitches. We haven't talked much about mechanics yet, more about the mental part of it and what are you trying to do every time you step up to the plate."
He's had more hits to deeper parts of the field this spring, and that part of his game is starting to pick up. But for manager Ron Washington, it's still about defense. And he liked what he saw last week in one of the early spring training games. Engel Beltre, the left fielder, lost a ball in the sun and Borbon was able to grab it.
"I was so pleased when he took that ball in left field that was lost in the sun," Washington said. "He wasn't a spectator. He was over where he was supposed to be, and when the left fielder couldn't find it he was there to take it. He's settled down after some errors the first two games and looks very good."
Borbon's job now is to create some momentum into the season.
"He can do so many things, but we just need him to do some of them," Pettis said. "He doesn't have to do all of them. But with his speed, he can run the bases and play defense on days when he's not hitting. Two of those three should work for Julio every day."
Richard Durrett covers the Rangers for ESPNDallas.com.