ST. LOUIS – It wasn’t just that Luke Jackson had a career-high six strikeouts while facing only seven batters Friday, becoming just the second Braves pitcher ever to do that in the Atlanta era. It was that he did it against a Cardinals lineup that has been on a serious surge and had pounded starter Mike Foltynewicz into the earliest exit of his career (2 2/3 innings) before Jackson entered.

“In three months I strike out six guys, and then in one day I strike out six,” Jackson said, smiling, “so I’m not sure how that happened.”

He was exaggerating, but not by much. Jackson struck out five and walked seven in 14 innings over his previous 15 appearances before Saturday, posting a 4.50 ERA in that span while allowing 17 hits and seven runs.

The right-hander’s six strikeouts in seven batters Friday was one-third of his previous season total of 18 strikeouts (with 11 walks) in 27 innings over 24 relief appearances, a rate of exactly six strikeouts per nine innings pitched.

Also, Jackson did have a pretty good idea what happened: the spike slider. Braves pitching coach Chuck Hernandez has urged Jackson in recent weeks to start throwing a slider instead of the cutter (cut fastball) that he’s used in the past. And the “spike” part of the grip he picked up from Triple-A pitching coach Reid Cornelius during Jackson’s recent minor-league stint.

Jackson entered the game with runners at second and third and two out in the third inning Friday, the Cardinals having already scored twice in the inning. He struck out the the first batted he faced, Paul DeJong, who had doubled in the four-run second inning when the Cardinals batted around against Foltynewicz.

“Right away I was able to come on with some guys on base and make some good pitches,” he said. “I was hoping to get a ground ball right there; I got a swing-and-miss. Man, I haven’t gotten many of those in three months. (Hernandez) keeps telling me I have a good slider, and I was, like, trying to trust it because it was new to me, I haven’t thrown one. This is the first year.

“So I was like, all right, and the past couple of outings it’s been kind of there for me, staying behind the ball.”

Jackson was a fastball/curveball/change-up pitcher in the past and would mix in the cut fastball.

“Chuck said, ‘Why don’t you turn that cutter into a slider and use it as an out pitch?’ I said I’ve never thrown one, but I can try,” Jackson said. “Two outings out of the pen, I came back up (from Triple-A) and it’s been here and there and he keeps telling me, ‘Listen, it’s good, just keep working on it.’ I’m starting to see it.

“It just kind of was a cutter (in Triple-A), and a cutter in spring training and last year. ... I throw a spike slider, which is different. Because I threw a spike curve I just kind of moved my fingers over, and it’s been working. Actually, Reid Cornelius down in Triple-A showed me that grip. He was like, ‘Listen, that’s what got me to the big leagues, you want to give it a shot?’ I was like, let’s go for it. Probably the most unconventional slider grip you can throw, but it’s working.”

He’d become more comfortable throwing the pitch, now it was a matter of fully utilizing it. Enter veteran catcher Kurt Suzuki, who was behind the plate Friday.

“Zuke put down the right fingers is what happened,” Jackson said. “I mean, yeah, one of those days where things are working, things are clicking, Zuke’s just throwing down money signs left and right. Can’t think him enough for that. I don’t think I shook (him off) one time.”

Jackson estimated that 50 percent of the pitches he threw Friday were sliders. After striking out DeJong, he struck out the side in the fourth inning – Dexter Fowler, Yakier Molina, Jedd Gyroko – then induced a leadoff grounder from Kolten Wong to start the fifth inning before striking out Randal Grichuk and pitcher Adam Wainwright.

Seven batters faced, seven outs, six strikeouts.

Jackson, 25, joined Mike Bielecki as the only Atlanta Braves pitchers to get six strikeouts in 2 1/3 or fewer innings, and the first major league pitcher to do it since Yankees reliever Dellin Betances on May 15, 2014.

“I think what was most impressive about that was what the Cardinal offense was doing up to that point,” said Braves knuckleballer R.A. Dickey, who faces the Cardinals in Sunday’s series finale. “He really did a good job of neutralizing that offense. And they’re a really good, scrappy club. They put the ball in play, they don’t strike out a ton -- they don’t have anybody with, like 30 homers, but you’ve got like eight with 15.

“They do a good job of putting the ball in play and he did a great job, saved our ’pen. Hopefully that’ll help us for the next couple of days.”