ST. LOUIS — Zach Eflin warms up before home games with the opening notes of Lynyrd Skynyrd's "Free Bird" piping through the Citizens Bank Park sound system, presenting the perfect ballad to match Eflin's relaxed demeanor on the mound.

The Phillies clubhouse may not have a  friendlier occupant than the laid-back Eflin. His 6-foot-6 frame exudes positivity, win or lose. But the Phillies thought Eflin was taking that  bright outlook onto the mound. He was perhaps a bit too nice.

The Phillies pushed him to be more imposing. They wanted him to attack and use his height to his advantage, look mean, and throw his four-seam fastball with authority. Eflin bought in, and the early results — a 0.71 ERA in two starts since being recalled from triple A — offer promise.

"Some of our pitching coaches in the organization have been working with him on being more aggressive and having more conviction and bringing some anger and physicality," manager Gabe Kapler said.

Eflin, who will  start Saturday against the Cardinals, is trying to make his case to stay in the rotation when Jerad Eickhoff returns later this month from the disabled list. It will be a challenge, since  Nick Pivetta and Vince Velasquez seem to be finding a groove. But Eflin,  with his new mind-set,  has at least made that decision a difficult one.

"I had always been pretty laid-back on the mound," Eflin said. "That resulted in me babying my sinker, babying my four-seam, and babying some off-speed pitches. Being able to stay aggressive on the mound and stay hungry on the mound has left an imprint on my mind to pitch with confidence. I've always kind of done it, but then I would take some off of my four-seam and two-seam. It's just using my change-up to offset my fastball instead of using my fastball in a different range of velos. It's really staying aggressive with my fastball, because when I'm aggressive with it, it has a different life and movement."

The righthander threw 55 four-seam fastballs in his last start, when he pitched 62/3 scoreless innings against San Francisco. The fastball's velocity ranged from 90.9 mph to 96.9 mph. His slowest fastball was nearly 2 mph faster than his slowest last season, and his average 94.2 mph was almost 1 mph faster.  He was no longer using his fastball like a change-up. He was strictly throwing it hard. And it resulted in six swing-and-misses. Eflin showed the conviction that Kapler was looking for.

"You notice a little bit more aggressiveness in his posture and in his facial expression, which is something we've been working on for a long time with Ef," Kapler said. "I think he attributes a lot of his success to a more aggressive demeanor on the mound. We all think that's going to play well for him."

Along with pitching with aggression, Eflin has altered his mechanics.  He now begins his delivery by standing on the third-base side of the pitching rubber. The adjustment came last month at triple A with the urging of IronPigs pitching coach Dave Lundquist and minor-league pitching coordinator Rafael Chaves.

The coaches tried to move Eflin to that side of the mound two seasons ago, but the righthander said he lost feeling for his change-up and sinker when he moved to the third-base side. They asked him to try again, telling him that his spin rates would be increased and his slider more effective if he started on the third-base side. Eflin trusted them and instantly felt comfortable. Kapler, a former righthanded hitter, said a pitcher as tall as Eflin can seem as if he's right on top of you when he moves to that side of the rubber.

"I noticed that everything is just a lot better on that side of the rubber," Eflin said. "Once I gained the confidence to pitch from that side and pitch effectively from that side and be able to use all my pitches, that's when it finally rang a bell that this is probably where I belong."