TRENTON – On stuff alone, Craig Heyer doesn’t exactly jump out at you. He doesn’t have a mid-90s heater or a buckling breaking ball like a few of his more hyped rotation-mates, and his name certainly doesn’t come up in conversations about the system’s elite arms.

What he does have, however, after 6 1/3 innings of two-run baseball in the Thunder’s 5-2 win over the New Hampshire Fisher Cats yesterday, is a tie for the third-best ERA in the Yankees organization.

The win also pushed the Thunder into a tie with New Hampshire for both first place in the Eastern Division and the best record in the league. After a sloppy 10-12 April, both feats seemed well out of reach.

Heyer attributed the rapid ascension to an upbeat clubhouse, which in turn has produced a brand of baseball that is more free-flowing than in the first month, when the team sometimes seemed mechanical.

“It’s been awesome. Everyone’s playing loose, playing relaxed. It starts at the top, actually, with Tony (Franklin). He’s loose and relaxed as well, so it’s kind of neat going out there every game and being confident, too.”

The final run yesterday – which scored on a bases-loaded walk after Heyer was yanked – upped his ERA from 2.77 to 2.78, and nudged him into a third-place tie with D.J. Mitchell, a member of last year’s Thunder rotation.

Accomplishing what he has so far has taken willingness to pound the strike zone over and over again with a low-90s fastball that features cutting and sinking action, as well as an ineffable ability to command.

“He’s been pretty consistent with what he gives us,” Franklin said. “ … He’s not going to overwhelm you with a lot of fantastic curveballs or velocity or anything, but the guy’s consistent, and that’s major league pitching.”

Entering yesterday, Heyer had walked just 15 hitters over his previous 140 2/3 innings, a total that spans last season. By comparison, teammates Manny Banuelos and Dellin Betances – who have each attracted considerable attention nationally – have issued 26 and 22 walks, respectively, this season alone.

Backing Heyer was a lively Thunder offense led by the resurgent Cody Johnson, who continued peppering line drives all over Waterfront Park. He scored three singles off of Blue Jays prospect Henderson Alvarez before coming up with his compulsory whiff of the afternoon.

His hits drove home two of the Thunder’s runs, and swatted the single that drove Alvarez from the game. Over his last 10 contests, Johnson, previously the definition of an all-or-nothing hitter, looks like a new man.

Since May 28, Johnson has hit a stunning .405/.419/.762 with three doubles, four home runs and 15 RBIs. He’s on a 10-game hitting streak, and was 8-for-14 in the series with New Hampshire. More amazingly, all of those eight knocks were singles.

The streak was spurred in part by Johnson lowering his hands in his stance, which has eliminated a pronounced hitch that plagued him over the first part of the year. Franklin thinks that, like the rest of his team, the designated hitter is carrying a renewed feeling of confidence onto the field.

“He makes an impact in our lineup now,” he said. “He’s a man to be reckoned with now, and I think the opposition knows that.”

NOTES: There’s no movement on the Austin Romine front. The catcher wasn’t in the lineup yesterday, and is not expected play today when the Thunder hit the road for four games against the Reading Phillies. … Catcher Ryan Baker got into his first game of the season last night, and immediately caught Darin Mastroianni, one of the league’s best base burglars, trying to take second.