Mateo's performance in the minor leagues earned him a trip to the Southern League All-Star Game in Montgomery, Ala., on July 10, which he started.
The right-hander was selected in the Rule Five draft last December by the Cardinals but was returned to the Cubs late in Spring Training. He won 10 games at Class-A Daytona a season ago and showcased a 3.21 ERA in 109 1/3 innings. He struck out 123 and walked 27.
West Tenn pitching coach Mike Anderson has worked with Mateo each of the past three seasons on the minor league venue and believes the 23-year-old was promoted at just the right time.
"He's a hot hand right now. Hopefully he'll carry that on to Chicago," Anderson said.
Mateo threw 88 pitches – 54 for strikes – in the win over Arizona. The Cubs (45-63) split the series at two games apiece after dropping game one of the doubleheader, 10-2, behind a wild outing from Carlos Marmol. Mateo became the first Cub rookie starter to win his major league debut since John Koronka did so last season in Los Angeles on June 1.
A former reliever at Class-A Lansing two seasons ago, Mateo began experimenting with a full-time starter's role for Daytona in 2005. He had modest success in the role, going 6-4 with a 3.28 ERA in 82-plus innings.
"This was only his second year of starting really," Anderson noted. "Last year at Daytona, we got him to develop his second and third pitches – changeup and curveball – halfway through the season."
Anderson described Mateo as being inconsistent with his off-speed pitches when he was first returned to the Cubs this spring, but, "Once he got going with us, he'd been real good of late," Anderson said.
"The last four or five starts with us, he really came around. He was throwing the ball more consistently. He was throwing his off-speed stuff for strikes. The light was starting to come on for him. He's always had good command of his fastball. He has good velocity and life to it and a little running action at times."
Mateo's fastball sits around 92 mph. He went on the disabled list in June with a strained pectoral muscle, but went 3-0 over his last five starts with the Double-A team.
"We took a precautionary response and made sure he was all the way back," Anderson said. "He's had no problems since then."
For Murton's part, the second-year left fielder bumped his average to .294 through 93 games this season. He finished July with a .360 average for the month, collecting 18 hits in 50 at-bats. Since the All-Star break, he is batting .395 in 13 games.
"I think I'm starting to learn that more so than anything, when you get in those opportunities, it's important to not try and do too much," Murton told reporters afterward. "I'm just trying to have a consistent at-bat time and time again."