The Blue Jays' No. 8 prospect allowed four hits over seven scoreless innings as Double-A New Hampshire defeated Altoona, 5-1, on Saturday.
McGuire (5-11) struck out three and walked three, throwing 52 of 97 pitches for strikes. The 2010 first-round Draft pick got some help from his defense, which turned three double plays.
"I kind of had pretty good fastball command and that pretty much set up everything else from there," McGuire said. "We were able to work both sides of the plate and up and down."
McGuire lowered his ERA in his first full season at Double-A to 5.78. The Eastern League is hitting .278 against him and he's surrendered 17 homers over 113 2/3 innings in 22 starts.
"It's all about my fastball command," McGuire said. "Anytime I've struggled this year I've fallen behind on my fastball, and when I missed over the plate I got beat. Tonight, I was able to stay out of the middle of the plate."
Success came easier last year, his first since the Blue Jays selected him 11th overall in the 2010 Draft. He was named a Florida State League midseason All-Star and went 9-5 with a 3.02 ERA across two levels.
"Baseball is a frustrating game, so if you get frustrated a lot you're in big trouble," the Virginia native said. "I just try to keep rebounding from start to start and keep treating each one as a new opportunity."
McGuire believes that the key going forward is the same thing that produced success on Saturday.
"Go out there and establish fastball command early and let everything work off that," he said. "I think when I get in trouble is when I stray away from the fastball too early in games."
Matt Daly followed McGuire to the mound and pitched a scoreless eighth. Trystan Magnuson, a 2007 first-round pick, gave up one run on a hit and two walks in the ninth.
Brad Glenn supported McGuire with two hits, including a two-run double, and John Tolisano added an RBI triple for the Fisher Cats.
Adalberto Santos was 3-for-3 with a run scored for the Curve.