The St. Louis Cardinals will test their top pitching prospects when they host the struggling Pittsburgh Pirates for a four-game series starting Monday.

Zack Thompson (0-0, 2.25 ERA) will get the call Monday as the first of three rookies scheduled to start in this series at Busch Stadium. Matthew Liberatore will pitch the first game Tuesday’s day-night doubleheader, and Andre Pallante will start Wednesday.

“You want stability in your rotation, but at the same time, these guys are pitching for something,” manager Oliver Marmol said. “And the competitiveness that comes with that is fun to watch.”

These rookies are filling in for injured starting pitchers Jack Flaherty (shoulder bursitis), Steven Matz (shoulder impingement) and Jordan Hicks (forearm flexor strain).

Thompson will make his first start and second appearance at the big league level. In his debut, he earned a four-inning save during the Cardinals’ 14-5 victory over the Chicago Cubs on June 3.

He allowed one run on three hits and a walk after taking over for starter Miles Mikolas.

“Young guys are full of energy. They’re fun to have around and fun to mess with,” Mikolas said. “It’s been good for us.”

Thompson, the 19th overall pick in the 2019 draft, was 2-2 with a 4.67 ERA in 10 starts for Triple-A Memphis this season.

While the Cardinals have won five of their last six home games, the Pirates come into this series with a season-worst six-game losing streak.

“We know we’re playing some young players out there,” Pirates manager Derek Shelton told ATT SportsNet Pittsburgh. “We have to just continue to learn and grow. It’s not for a lack of effort. We’re playing hard, we’re doing things, we have to execute.”

They will counter Thompson with Mitch Keller (2-5, 5.26 ERA), who posted a 2.65 ERA and struck out 18 batters in 17 innings in going 2-0 in his last four outings.

Keller delivered six strong innings in his last start, a 3-1 loss to the Detroit Tigers. He struck out seven and allowed just one run on four hits and two walks while relying heavily on his newfound sinker.

“I think I still don’t have all the feel in the world for that pitch yet,” Keller said. “But it’s just such a good pitch with so much movement that it just gives me the confidence to attack the zone with it, even if I am missing arm side or missing down with it.”

In his first start of the season on April 9, he sustained a 6-2 loss to the Cardinals. He allowed four runs on six hits and two walks. He struck out four.

Keller is 2-1 with a 4.26 ERA in five career starts against the Cardinals.

The Pirates and Cardinals are braced for triple-digit temperatures for this series.

“We’re going to St. Louis and it’s supposed to be 100, 102 and 100 and we play a doubleheader on the 102 day,” Shelton said. “So just make sure we take care of our bodies, make sure we stay hydrated and make sure everybody gets involved.”

–Field Level Media