MESA, Ariz. -- Junior Lake and Starlin Castro are so close, they could be brothers.
There's a joke around camp that the Cubs infielders could be twins.
As members of the club's Dominican Summer League team in 2007, the pair was rarely more than 45 feet away from each other when they took the field. They were never more than five feet from each other when they were off it.
Lake and Castro share a friendship and a passion for the game, which is great for Chicago. But they also share a position: shortstop. And at times, that can be tricky. Back in the Dominican Republic, the duo would switch back and forth between second base and shortstop every other game in the summer league.
When they played in rookie ball in Mesa, Ariz., Lake was at shortstop and Castro was at second base in the first half of the season. They switched positions in the second half.
It's almost as if they have been flip-flopping since birth.
Castro, who will be 22 on March 24, is the three days older than Lake. He's also what Lake aspires to be: a big leaguer. But if all goes according to plan, the baseball buddies will be take the field at Wrigley Field together one day in the future.
"Castro is a great guy, and he has always been like that with me since we met," Lake said. "He's never showed a big ego and he's always been a good friend to me. We've always played together and we know how the other operates on the field. We know where the other will be without even looking."
Lake has been working primarily at shortstop this spring, but he's open to playing second base again or shifting to third base if the move gets him to the big leagues faster. He's also not against playing any of the three outfield positions, even though he has never played them.
"One guy is in front and one is behind, but it's not like they can promote two people for the same position at the same time," Lake said. "Castro was able to develop his abilities faster than I was, but he doesn't think he is better than me and I don't think I'm better than him. Neither of us is better than the other."
Lake is right. But there is no denying that Castro, who entered the club's academy in the D.R. two months before Lake, is more advanced at this point. Last season, Castro hit at least .300 for the Cubs for the second consecutive year, and amassed 207 hits along the way. By contrast, Lake spent last season in the Minor Leagues, and was playing with Class A Advanced Daytona when Castro was promoted from Double-A Tennessee to the big leagues in 2010.
"I told him to be ready," Castro said. "You never know. I told him, 'I know you can play in the big leagues, you know you can play in the big leagues. Do your job.' I was surprised when I got called up. That's what I tell him. You won't even know. It'll surprise you."
It appears that Lake, ranked the 10th-best prospect in the organization by MLB.com, still has some work to do before he gets a big league call. Last season, he hit .279 with 12 home runs and 59 RBIs for Daytona and Tennessee. He also combined to hit 21 doubles, six triples and scored 80 runs.
Last fall, Lake hit .296 for the Mesa Solar Sox in the Arizona Fall League and began learning to speak English, thanks in large part to his AFL roommate, Tyler Saladino, a shortstop prospect with the White Sox.
"Junior is bright, he's got a lot of talent and he's a young guy, all of the positive adjectives to describe a player like him," said Oneri Fleita, the club's vice president of player personnel. "Remember, we signed him at 16 in 2007, and he would only be a senior in college right now. He went to Double-A and he's making progress. He's actually ahead."
Cubs manager Dale Sveum likes what he has seen from Lake in spring training and said he can see the young man playing third base one day. Truth be told, Sveum can probably see a guy like Lake playing any position on the field.
"The guy's a specimen," Sveum said. "He has some kind of athletic body. He's got to just keep playing. He's a guy who needs at-bats in games and stuff like that. That's a pretty good talent coming."
Lake is listed at 6-foot-2 and 215 pounds, and Fleitas estimates Lake has grown at least three inches and put on 20 pounds of muscle since the club signed him five years ago. Lake is also maturing in other ways. He's come to realize that his stay on the fast track to the Major Leagues is directly related to his ability to slow things down on the field.
"Sometimes, I've tried to do things too fast. And when you do that, you can make errors -- and that leads to even more errors," Lake said. "You have to stay calm. You concentrate and anticipate what's going to happen. When a play happens, you knew it was a possibility.
"The higher levels, the faster the game is and the more focus you need to have for things to go the right way. The higher you get, the more your mistakes matter."
Lake's development also includes an improved approach in the batter's box.
"He sees the ball better," Castro said. "When I played with him, [pitchers] threw a lot of breaking balls in the dirt and he would swing. Now, he doesn't swing. He's more patient. He's coming along pretty good."
For the record, Lake said it doesn't matter if he lines up to Castro's left, his right or behind him -- as long as they get a chance to play in the big leagues together. But Lake is also careful not to sound too brash. Alfonso Soriano, one of Lake's mentors, has encouraged the young infielder to respect the game and stay humble.
Soriano's message to Lake is a simple one: Today's hero is tomorrow's goat. Nobody knows that baseball truth better than Soriano.
"My goal is to go from Double-A to the big leagues, but I have to keep working," Lake said. "It's all about work. They believe in me and I believe in myself."