JUPITER — The pitching surplus to open Marlins camp was a sure sign that there were a lot of things up in the air. It’s down to the home stretch: nine games to go, 20 of 37 pitchers still suiting up and a big cloud of uncertainty over what Mike Redmond’s five-man rotation might look like come April.

Jacob Turner’s start on Tuesday only makes it more difficult.

The third-year major-leaguer acquired from Detroit last season was thought to be one of the answers, but being taken advantage of by the St. Louis Cardinals’ batters in his third consecutive start might be too much risk for any reward.

“Personally, I feel like I’ve gotten better every outing mechanically,” Turner said. “That’s just coming from me as far as how I feel.”

The 21-year-old worked quickly through three innings of Tuesdays 5-4 loss to the Cardinals, though the smooth road found bumps in the fourth and fifth.

Three long fly balls to center fielder Justin Ruggiano and right fielder Giancarlo Stanton finally caught up to Turner. Allen Craig put the Cards on the board with a home run that sailed clear over the fence at Roger Dean Stadium, leaving Ruggiano and Stanton helpless.

Turner went from a scoreless game with one hit, to adding seven hits, four earned runs and a walk to his line for the day. The right-hander struck out two.

“I think I was leaving a few pitches up in the zone and that’s not really my game,” Turner said of the long balls. “Keeping the ball down is my game [and] getting ground balls. Unfortunately, I left a few pitches up and they were able to take advantage of them.”

Setting aside Ricky Nolasco, who will anchor the Marlins’ rotation, those who will follow him have less combined major-league experience than Nolasco’s seven years.

Henderson Alvarez, 22, and Nathan Eovaldi, 21, are both making strong impressions on the Marlins staff and are expected to fill two of the spots with their collective four years. Turner can add two more years of experience.

With the Marlins in 2012, he posted a 3.38 ERA through seven starts, holding batters to a .208 average.

Though Redmond was encouraged by Turner’s early work in his Tuesday start, there isn’t much time left at camp to prove that the slow and steady spring progression is going in the right direction. At least in time for April’s opener.

“His first outing, he was all over the place with his command; [he] just looked really uncomfortable,” the manager said. “He looked much better up there today. He looked more confident, and he was around the zone the whole day.”

In Turner’s previous outing, also against St. Louis, he allowed two hits and a walk in three innings. It was down from six earned runs and three walks in his spring debut over a third of an inning on Feb. 28.

Even with the long balls, Redmond argues that a strike is a strike, and he’s happy to see Turner get his pitches in the zone.

“That’s what we were looking for was for him to come out knowing what’s at stake and come out and pitch well,” Redmond said. “I definitely feel much better about that. I’m excited about the way he came out those first three innings.”

The start still leaves the door open for other arms that are doing things right this spring. Veteran Kevin Slowey boasts a 2.63 ERA and is 12th among pitchers in the league with at least 122/3 innings pitched. Slowey will get a minor-league start in inter-squad action on Thursday’s day off.

Also in the mix is John Maine, who has started 105 games in his seven-year major-league career.

His last big-league appearance was in 2010 with the Mets. Maine will follow Wade LeBlanc’s start on Wednesday.