Selected 25th overall in the 2011 Draft, Ross has been on the disabled list since May with a sore right shoulder.
But on Monday, the 19-year-old struck out three batters and issued four walks over four hitless innings in the Class A Short-Season Eugene Emeralds' 7-5 win over the Tri-City Dust Devils.
"I'm at 100 percent now," he said. "I'm just building up my innings again. I felt pretty good and I was happy with the results. ... If I go to [Class A] Fort Wayne again, that's good, but if not, I'll stay here."
Ross walked the leadoff hitter in the first two innings, but neither one advanced past second base. He issued a one-out free pass to Kyle Von Tungeln in the third inning, but the center fielder was thrown out at second base. And after Tom Murphy reached on third baseman Gabriel Quintana's throwing error, he walked Derek Jones in the fourth.
"My arm felt good, but my command was a little bit shakier than usual. I felt good, though," he said. "My fastball was there. I only threw my changeup a few times, but my slider was pretty good. I tried to stay down in the zone, make good pitches and get ground balls."
Ross went 0-2 with a 6.26 ERA in six starts with Fort Wayne before going on the disabled list after his start on May 4.
He went through a three-week throwing program in Arizona, throwing first from 60 feet, then 90 feet and eventually 120 feet. After three bullpen sessions, the team decided he was ready for live action again.
The 6-foot-3, 185-pound farmhand returned to competitive action with the Padres' Arizona League affiliate seven weeks after he was originally diagnosed. The organization has been building him back up ever since.
He was assigned to the Northwest League on July 25 and he tossed a scoreless inning for Eugene against Vancouver. Since then, San Diego's No. 9 prospect has been gradually going deeper into games.
He went two innings against Salem-Keizer four days later in his second start for the Emeralds, and he allowed one run over 2 1/3 frames at home vs. the Canadians on Aug. 3. Five days later, Ross allowed two runs on four hits and a walk over 3 1/3 innings on the road in Yakima.
"I think it was just a little bit of overuse," said Ross, the younger brother of A's pitcher Tyson Ross. "Pitching in high school was different from pitching here every fifth day. [My shoulder] was just not fully ready for that everyday grind.
"It's different from pitching once a week and then having however many days off. You're throwing every day to get the work in, but you're also trying to stay healthy and ready for your next start."