ST. LOUIS -- Mitch Keller's performances since he was recalled from a month and a half at Triple-A have been decent, but still pointed to some of the concerns that led to his option in the first place.

But on Friday, Keller shut down the Cardinals over five scoreless innings to help the Bucs snap out of a skid with a 4-0 win at Busch Stadium.

It was a statement win for the former No. 1 prospect in the Pirates’ system. The outing was the first scoreless start of five innings or more for Keller since May 29 vs. the Rockies, which also had marked his last win until now.

A major key to Keller’s success -- fastball command -- trended in the positive on Friday, as the 25-year-old drew a career-high 10 whiffs on his four-seamer. Six of those misses came up in the zone, including two on balls out of the zone that were too enticing for the Cardinals’ hitters.

“That was kind of a scouting report was that that’s his best pitch -- his fastball -- so trying to get that down,” said Cardinals right fielder Lars Nootbaar, who had three hits on Friday. “Obviously, when he goes up, he can kind of beat us because it’s got life on it.”

Keller all but scrapped his curveball, which he’s paired with his slider to give a different look to his breaking stuff. Against a right-handed-heavy lineup, he also threw his changeup only once. It was virtually all fastballs and sliders on Friday, and they played.

“I think that speaks to the fastball execution,” manager Derek Shelton said. “That’s a good lineup, and he was able to get through them and kind of mix and match.”

Keller’s day wasn’t without some testing moments. The right-hander loaded the bases on two singles and a walk in the second inning before inducing a pop fly in foul territory from Cardinals starter Miles Mikolas. Then, with a two-run lead and two outs in the fifth, Keller faced his biggest challenge.

With runners on the corners and one out, Paul Goldschmidt and Nolan Arenado were due up for St. Louis. Keller had handled them with fair ease earlier in the game -- a flyout and double play off Goldschmidt and two strikeouts of Arenado -- but he recognized these are two of the best players for a reason.

Goldschmidt sent a first-pitch slider on the outer half of the plate to third baseman Ke’Bryan Hayes, then Arenado missed the barrel on -- what would you expect? -- a high-zone four-seamer.

“It’s obviously a huge confidence booster and huge for the team,” Keller said. “Those guys do any sort of damage there, the game’s totally different. That’s huge."

“You have to get through those innings, and I think those are the innings in the past where the execution of the pitches haven’t been as consistent,” Shelton said. “And today, he was able to get them. … That’s extremely important. We talk about moving forward -- those are the victories that we have to isolate and talk about.”

Of course, the Pirates’ shutout effort wasn’t the work of just one pitcher. The Pirates sent Duane Underwood Jr., who began the season more in relief of short, troublesome starts, in to protect a three-run lead, and he went 1 2/3 innings before David Bednar backed him up with 1 1/3 innings without any damage. Chris Stratton closed the door in the ninth.

“Guys picking up guys: Duane picked me up for two innings, then Bednar picked him up, which is just how it goes,” Keller added. “When everyone is clicking like that, wins like this come.”

Wins for Keller also come when the right-hander can put the pieces of his game together. He was inconsistent in accomplishing that earlier this season, leading to a demotion to Triple-A as his ERA jumped above 7.

Now, he feels like he’s on the right track, and he wants to finish his first full 162-game season as strongly as he finished Friday’s outing.

"It feels amazing, honestly, after everything I've been through this year working back,” Keller said. “I felt really good in my last [three] starts. The results weren't there, and I think I just came full circle tonight. Just attacked the zone and got hitters out."