The Mariners prospect pitched seven hitless innings as the Double-A Jackson Generals pulled away for a 6-0 victory over the Jacksonville Suns.
Gillheeney (1-3) threw 112 pitches as he matched his longest outing of the season and registered his first Double-A win in seven outings this year. He called the start the best of his professional career.
"I felt good tonight," Gillheeney said. "I didn't really try to do anything out of the ordinary. I was just trying to go out there and do what I try to do every time, which is get early contact and get my team in the dugout to hit. Tonight, we just had a great, great win. I had great defense behind me and I executed pitches when I needed to."
Gillheeney walked four, including the leadoff batter in the second, fourth and seventh. His most difficult inning was his last, when he had runners on the corners with two outs before getting Paul Gran to fly out.
"I was doing too much nibbling at the corners and I winded up walking two guys," he said. "Our catcher [Jesus Sucre] came out and calmed me down a little bit. He said, 'Just settle down and get ahead of this guy, get ahead of the next guy.' It ended up working out where I got through the seventh."
The 23-year-old left-hander turned over a 5-0 lead to Stephen Penney, who pitched a scoreless inning but surrendered the Suns' only hit -- a leadoff double to Neil Sellers.
"We were all kind of hoping we could hold it, but Penney's been a great pitcher for us all year and I'm sure he felt pretty bad about it," Gillheeney said. "But he still got in there and got the job done and didn't give up any runs. I wasn't really too upset about it."
A 2008 eighth-round Draft pick, Gillheeney went 6-5 with a 5.35 ERA for Class A Advanced High Desert before being promoted to Jackson. He posted a 6.68 ERA over 32 1/3 innings for the Generals prior to Saturday's outing.
"I was getting my off-speed pitches over for strikes when I needed to and I was throwing backwards in counts," Gillheeney said. "I'm not a flamethrower, so that's my mentality when I get on the mound anyway. Tonight was just execution."
Looking back on his second full professional season, Gillheeney said he's refined who he is as a pitcher.
"What I've learned most is really trying to attack hitters and not trying to pitch away from contact," he said. "Really trying to get early contact in the count and not fall behind hitters. Because at this level, they make it hurt.
"Executing off-speed down the in count is also big for me because, like I said, I'm not a flamethrower that can throw a fastball by guys. Those two things have been the most important things I've learned and are things that, start-by-start, I've been trying to get better at."