CHICAGO -- Tyler O'Neill 's scorching-hot start lifted him all the way to the Majors.

The Cardinals promoted O'Neill, one of the hottest hitters in the Minor Leagues and the Cards' No. 4 prospect per MLB Pipeline, prior to Thursday's 8-5 loss to the Cubs at Wrigley Field. O'Neill got into the game as a pinch-hitter in the fifth, striking out to end the inning.

"Everything I worked for my whole life came down to that one moment," O'Neill said of the callup before the game. "I'm going to try to make the most of every chance I get and leave nothing out on the field."

The club originally planned to promote O'Neill for Wednesday's game, before it became the second postponement in three days due to inclement weather at Wrigley Field. That gave St. Louis another day to officially recall the slugger from Triple-A Memphis and make a corresponding move, which was the optioning of right-hander John Brebbia to Memphis.

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O'Neill could provide insurance for center fielder Tommy Pham, who suffered a minor right groin injury in Tuesday night's 5-3 win.

Pham underwent a variety of tests on his right groin on Wednesday, and he was held out of Thursday's lineup as a precaution.

The 22-year-old O'Neill brings immense raw power, sneaky speed and an ability to play all three outfield positions. If Pham is fine, O'Neill will give the Cardinals a fifth bench player for the first time this season. The team had been carrying eight relievers, but saw no need for an additional arm during the upcoming schedule. The Cards have three off-days in the next 13 days.

Manager Mike Matheny has rarely used his eighth reliever in the early going, while routinely running out of bench players late in game. Matheny couldn't replace Pham in the ninth inning on Tuesday after Pham's groin tightened in the cold weather, because the skipper had already exhausted his reserve options. Twice over the season's first two weeks, Matheny used starting pitcher Luke Weaver as a pinch-runner.

O'Neill was summoned to Chicago on Wednesday, as Pham underwent testing on his groin. Neither were in the starting lineup for Thursday's series finale.

Pham isn't expected to miss much time, meaning most of O'Neill's playing time would likely come as a pinch-hitter or late-game replacement.

"On all the off-days we have, we always talk about having the extra pitchers, and I love the arms," Matheny said. "We were thinking about this before, but as soon as Tommy went down, I had the trainers starting making calls. Let's have another position player here."

In O'Neill, St. Louis plucked the most locked-in hitter from a Memphis team sizzling at the plate in the early going. The right-handed-hitting O'Neill is tied for the Minor League lead in home runs with six, and he was hitting .388/.385/.837 with 18 RBIs across 12 games.

"For me, it was a couple of different things that all clicked at the same time," O'Neill said.

Acquired from Seattle last summer for left-hander Marco Gonzales , O'Neill entered his first Spring Training with the organization as a candidate to make the club. He hit .246/.321/.499 with 31 home runs in his first season at Triple-A in 2017, including 12 home runs in 37 games for Memphis. Club officials expressed disappointment after oblique and hamstring injuries limited O'Neill to just 12 at bats in Grapefruit League play this spring.

"I'm not really looking back to spring. That's over and done with. I went to Memphis with a positive mindset and did my thing," said O'Neill. "Everything was really clicking for me. Now we're going to see if I can do it here."