But former Jupiter teammates Justin Nicolino and Anthony DeSclafani -- who both moved up earlier -- had cautioned Heaney even before he joined the Suns that Southern League hitters don't miss bad pitches.
In his second Jacksonville start, the ninth overall pick by the Miami Marlins in the 2012 Draft found that out first hand.
Tennessee broke the scoreless streak with three first-inning runs and scored in each of the next two innings as well, battering Heaney for nine hits and five runs in three innings.
"I just didn't do a good job competing, and Tennessee has a very good hitting team," the left-hander said of his Aug. 6 misadventure. "When you don't have your best stuff, you have to try to get ahead in the count and work with what you have. I didn't do either."
The Minor Leagues are all about learning, though, and the No. 52 prospect on MLB.com's Top 100 list took advantage of the lesson.
Heaney allowed just eight hits and two runs over 11 2/3 innings while winning his next two starts and is 3-1 with a 3.05 ERA for the Suns despite the one bad outing.
"It's hard to say and it certainly isn't fun, but maybe you need a game like that," the Marlins' No. 3 prospect said. "It gets you refocused."
Heaney, 22, has certainly been locked in most the season, although he got a late start after straining his lat muscle this spring. The former Oklahoma State standout was 5-2 with a 0.88 ERA in 13 outings for Jupiter, finishing his stay in the Class A Advanced Florida State League with 26 straight scoreless innings.
"The streak was cool," Heaney said. "It was exciting and I took pride in it. But it wasn't something I was concentrating on. I knew it would end."
It did with a bang against Tennessee, but now Heaney is trying to help pitch Jacksonville, which leads the second-half standings in the South Division, to the Southern League playoffs.
"We've been playing really well and it's been a lot a fun," said Heaney, who pitched in the Class A South Atlantic League playoffs last year for Greensboro. "It's great to have something to play for. That's what you always want."
With outfielders Christian Yelich and Jake Marisnick promoted to Miami, pitching is the key and the Suns have plenty of it.
The Jacksonville rotation has four of the Marlins' top prospects -- with No. 3 Heaney followed by Nicolino at No. 4, Adam Conley at No. 5 and DeSclafani at No. 15.
The Suns also have a deep bullpen anchored by Michael Brady, who leads the Southern League with 21 saves and has a 1.49 ERA.
"I don't think any of us [in the rotation] have a set pitch count, but there is no need to really push it with the relievers we have," said Heaney, who is a combined 8-3 with a 1.42 ERA in 17 games for the Suns and Jupiter.
The former NCAA strikeout leader has a fastball that can reach the mid-90s when he needs it, as well as an effective changeup and potentially deadly slider.
"My changeup has been really good and my slider is just starting to come around again now," said Heaney, who has 80 strikeouts to 23 walks in 82 1/3 combined innings and has held opponents to a .208 average. "I hope to finish strong with it."
Double-A hitters may not miss many mistakes, but they are still at a disadvantage against a pitcher with all of Heaney's weapons.
Streaks end: Mississippi catcher Christian Bethancourt had his team record on-base streak end at 40 games and his hitting streak snapped at 16 games when he went 0-for-4 at Pensacola on Friday. The Atlanta Braves' No. 3 prospect batted .338 with 10 homers and 27 RBIs during the on-base streak, which dated to June 13. Bethancourt, 21, drew 13 walks during the stretch, five times keeping the streak alive that way. The old Mississippi record for reaching base safely had been 38 games and was set by Willie Cabrera in 2009.
No reward: Pensacola right-hander Robert Stephenson, ranked No. 19 among MLB.com's Top 100 prospects, was sailing along with a 1-0 lead against Mississippi through six innings Friday in his Double-A debut, having allowed just two hits. But Cincinnati's No. 2 prospect walked the first two batters of the seventh and the Pensacola bullpen couldn't come through, pinning the 20-year-old with the decision in a 5-1 loss. The Southern League is the third level this year for the first-round pick in the 2011 Draft. Stephenson is 7-6 with a 2.69 ERA in 19 combined starts, posting 123 strikeouts to 25 walks in 103 2/3 innings.
Up and down: Birmingham left fielder Brandon Jacobs went into a deep funk after getting a hit in his first 17 games with the Barons, suffering through a 4-for-47 skid. But the Chicago White Sox's No. 8 prospect showed signs of finding his missing batting eye by going 2-for-4 on Sunday against Tennessee. Jacobs, acquired from the Boston Red Sox for veteran lefty reliever Matt Thornton, was hitting .233 in 31 games with the Barons.