The Padres' top pitching prospect struck out a career-high nine batters and allowed five hits over six scoreless innings as Tucson lost to Sacramento, 3-2, on Wednesday.
Kelly, who didn't figure into the decision, did not issue a walk for the Padres. After allowing a double to Michael Taylor with one on and no outs in the fourth, Kelly buckled down to retire the final nine batters he faced, six via the strikeout.
"Early on, my fastball command wasn't very good," Kelly said. "I tried getting through with my offspeed stuff and it got me through some jams. As the game went on, I got a little better with the fastball command. I think the fastball kicked in and I had a good curveball which got me out of some jams. Later on in the game, just having a good mix is what did it for me."
Kelly previously fanned eight batters twice while pitching for Double-A Portland in July 2010. The 22-year-old Floridian has yet to earn a decision in the Pacific Coast League, but has a 2.25 ERA in two starts with 14 strikeouts for the Padres.
"I'm just trying to get people out whether it's a strikeout, a groundout or a popout," the former first-rounder said. "Tonight I had a good mix going and got those strikeouts."
Kelly outdueled Jarrod Parker, Oakland's top prospect, who allowed two runs -- one earned -- on nine hits while striking out six over six innings for the River Cats. The matchup provided no extra motivation for Kelly however.
"I'm not facing him but it's always fun to face someone like him," Kelly said. "It's going to be low-scoring and you know you're going to get a good performance out of him."
Brad Boxberger, the Padres' No. 12 prospect, took the loss. He allowed two runs on two hits in the ninth.
Derek Norris, the A's No. 7 prospect, was 2-for-4 with a run scored and is batting .393 for Sacramento.