Mateo was a non-drafted free agent in 2001 that began the past season in the Daytona bullpen. In 16 appearances in relief, he was 4-1 with an ERA of 3.00. Moved into the starting rotation in late May, Mateo proceeded to win six starts to finish the year with a 3.28 ERA in his 16 starts while logging 82 1/3 innings there. Overall, he was 10-5 with a 3.21 ERA in 109 1/3 innings.
Most impressive was Mateo's strikeout to walk ratio in 2005. He punched out a team-high 123 batters and walked only 27. This was essentially Mateo's first year as a starter. Prior to this season, the 22-year-old made 52 relief appearances at Class-A Lansing a year ago and appeared in 18 games from the Rookie Arizona League Mesa Cubs' bullpen in 2003. He also spent time in the Dominican Summer League in 2002.
The transition into the rotation this year went well for a number of reasons. Not only did Mateo prove he could handle the workload of a starter, it gave the Cubs a good look at another potentially strong arm capable of adding more depth to a farm system already stocked with top tier pitching prospects.
"I think the numbers speak for themselves," said former Daytona broadcaster Bo Fulginiti. "The Cubs made a wise decision by putting him into the rotation. His out-pitch is a nasty slider, and he throws low and away to right-handers. He's also got a great fastball, plus-91 mph on the gun, and a great attitude."
Other strong points for Mateo this season were his ability to bounce back after bad outings. He lost back-to-back starts only once and won his final three decisions of the season.
Fulginiti noted, "He doesn't let a bad outing affect him on the mound. I can remember only one bad outing he had, and that was against Jupiter on July 1. He didn't get out of the first inning, but afterward he reeled off a couple of wins in his next three starts. To his credit, he's the type of pitcher who bounces back quickly."
Of course, there are the inevitable weaknesses to Mateo's game. He struggled against left-handed hitters at times this season, allowing 40 hits in 36 2/3 innings. In addition, he often fell behind early in starts, allowing 14 first-inning runs for an 8.40 ERA in that window.
"He also needs to continue to log more innings as a starter," added Fulginiti, the second-year play-by-play voice of the Cubs. "This was really his first year starting. He was a completely different pitcher in the last month of the season, because he was finally comfortable with the 100-plus pitch count workload."
Mateo closed out the year with a 1.72 ERA and .180 opponents average in his last six starts, in which he was 3-0. For the full year, opponents batted .240 off him in his 32 appearances.
"He's got a lot of untapped potential," Fulginiti said. "It's somewhat tough to figure out as he's just now popping up on everyone's radar, so nobody really knows how good he can be yet. I think he has a lot of talent."