With two away, New Orleans catcher Robinson Cancel hit a sharp grounder back up the middle that Mateo deflected to shortstop Ronny Cedeno, who alertly fired to first base for the final out in the inning.
Mateo (), a 24-year-old right-hander who made 10 starts for Chicago last season, was examined by Iowa team trainer Bob Grimes. X-rays were negative, Iowa manager Buddy Bailey said.
"It hit him around the wrist and he had some pain, but he got X-rays and he's good," said Bailey. "He's just got a bad bruise."
"I feel better now," Mateo said after the game.
Mateo missed over two months of the season with shoulder soreness. He is 2-3 with a 4.05 ERA through 40 innings with Iowa.
"He was hurt all Spring Training and didn't start throwing again until probably the end of May," said Iowa pitching coach Mike Harkey.
"His biggest thing is end of the season healthiness."
Mateo was 7-4 with a 2.82 ERA while making 17 starts at Class AA West Tennessee a season ago before earning a big league promotion to Chicago, where he was 1-3 with a 5.32 ERA while logging 45 2/3 innings.
The St. Louis Cardinals selected Mateo in the Rule Five Draft in December of 2005 after he won 10 games and posted a 3.21 ERA in 32 appearances, including 16 starts, at Class A Daytona the previous season.
Mateo was returned to the Cubs the following March.
"The stuff that we're working on here is getting him to be more consistently on top of the ball so that he can throw the ball downhill," Harkey said.
"It's been tough," he added. "He actually did well in the big leagues, so he's had some success at the major league level. He's a good student."