Towles took the Astros by storm in September of 2007, going from Class A to the Majors in a span of a few months and he tied a club record by driving in eight runs in a game in St. Louis. The next spring he was the can't-miss kid and came to camp in 2008 with the world in his mitt.
Two years later, Towles is still trying to establish himself in the Majors and finds himself across the clubhouse from Castro, the current top prospect. Drafted in the first round only months after Towles struggled at the start of the 2008 season, Castro is competing with Towles to be the Opening Day starter behind the plate.
It's is one of the most intriguing, and perhaps the most important, battles of the spring.
"It's huge," Astros general manager Ed Wade said. "If we thought our catching situation was significantly deficient, we would have addressed it during the offseason. Where we thought we had deficiencies during the offseason, we addressed them, and we didn't do anything at catcher because we think J.R. and Jason and [Humberto Quintero] have the ability to give us a solid catching core."
Houston has a Gold Glove center fielder in Michael Bourn, a polished defensive shortstop in rookie Tommy Manzella and a steady defender at second base in Kaz Matsui. But a team that's strong up the middle must have a top-notch defensive catcher.
Ivan Rodriguez and Quintero shared the catching duties last year, with Towles and Chris Coste getting some time behind the plate. Rodriguez was traded, and Quintero is returning to back up either Towles or Castro.
"The guy that puts the fingers down behind the plate has to have the confidence in the pitching staff and has to have the confidence of the manager and the pitching coach, and we think that particularly Castro and Towles, the two young guys, have the capability of stepping up and being a solid No. 1 catcher," Wade said.
Castro, drafted No. 10 overall in 2008 out of Stanford, is considered the club's catcher of the future. He hit a combined .300 with 10 homers and 73 RBIs last year in his first full season in professional baseball when he split time between Class A Advanced Lancaster and Double-A Corpus Christi.
In a busy year that saw him traveling the globe, he also played in the All-Star Futures Game, for the U.S. team in the IBAF World Cup in Italy and in the Arizona Fall League. The Astros finally shut him down in October.
"Similar to last year, I'm coming in with my ears and eyes open, and trying to take everything in and learn as much as I can, and continue to get my work in and do my best out there," Castro said. "Hopefully, I can show some people that I can play."
Towles, 26, has split two seasons between Triple-A Round Rock and the Astros since hitting .375 in 40 at-bats with Houston in 2007. He batted .199 with two homers and three RBIs in two stints with the Astros last year, but homered twice off Pedro Martinez on Sept. 30. He started nine of the team's final 17 games and had six hits in his final 16 at-bats.
"Like I've said before, I'm not going to wake up in the morning and not be able to hit," Towles said. "It's just that I had to go down to Triple-A and find my swing, and did well, and got some more playing time in the latter part of September and proved I can hit up here."
For Towles, a new coaching staff means somewhat of a clean slate and chance to prove himself in front of a new manager.
"I always think there are areas you need to improve on no matter what, but right now it's building the relationship with the pitcher so that they have that confidence in me back there and just swing the bat like I'm capable," Towles said. "[Castro] was a first-rounder and was a No. 1 and obviously has what it takes. He's definitely good enough to play up there. It's one of those things where we're going against each other and he's going to push me a little bit and I'm going to push him, and we'll make each other better."
Castro has yet to play above the Double-A level and isn't one to look ahead. If he has to start the season at Round Rock, so be it. But if he's behind the plate when the national anthem is played on Opening Day, even better.
"That would be a dream come true and something I've worked towards since I was a little kid," Castro said. "I'm not really thinking about that quite yet. Hopefully at some point down the road, whenever that may be, I'll be ready for it and I'm excited for camp to get going and excited for what's to come."
Brian McTaggart is a reporter for MLB.com This story was not subject to the approval of Major League Baseball or its clubs.