ST. LOUIS -- In a season already full of memorable moments for the Cardinals, Sunday undoubtedly qualified as the low point and proved to be a forgettable day full of loathsome losses.

Within a 3-hour and 50-minute stretch Sunday, St. Louis lost starting pitcher Jack Flaherty to another shoulder injury, lost an early 5-0 lead, lost 6-5 in 10 innings to rival Chicago and ultimately lost a home series to the rebuilding Cubs. Afterward, the Cardinals struggled to describe which loss hurt most, but Flaherty not coming back out for the third inning because of a case of “dead arm,” certainly cast the most doubt over how the team will deal with losing another key cog from its starting rotation going forward.

Flaherty, who missed the first 2 1/2 months of the season with right shoulder inflammation, left Sunday’s start after two innings with more trouble in his right shoulder. Manager Oliver Marmol said Flaherty didn’t complain of pain but instead stiffness and a lack of feeling in his shoulder after throwing just 49 pitches in an outing initially scheduled for 80+. It is yet another injury concern for Flaherty, who has been dealing with shoulder and oblique issues since starting the 2021 season with an 8-1 record.

“He came in after that second inning and said that nothing was hurting, but he had a dead arm,” Marmol said. “Nothing was coming out the way he wanted it to. A little stiff, but nothing in the same spot that we’ve been working on this whole time. We weren’t going to risk it and we took him out. … More dead [in the arm] more than anything and a little stiff, but nothing reoccurring from what he was experiencing before.”

With Flaherty likely headed for another stint on the IL, St. Louis' options to fortify the rotation are somewhat limited with Jordan Hicks and Steven Matz already out. Hicks is close to returning, and he has been working in two Minor League outings but might work out of the bullpen when he returns. Matz, who was signed to a $44-million free-agent deal in the offseason, will make a rehab start Tuesday, but he is likely double-digit days away from a return after not pitching at the MLB level since May 22. Matthew Liberatore is 2-1 with a 4.00 ERA in four starts and is the most likely replacement for Flaherty in the rotation, but the Cardinals have been leery about overexposing their No. 3 prospect thus far.

Flaherty left after St. Louis had a 2-0 lead, and it eventually pushed its edge to 5-0 on solo home runs by Brendan Donovan, Paul Goldschmidt and Juan Yepez in the third inning.

But that lead was erased not long after when Chicago rallied for five runs off relievers Nick Wittgren and Johan Oviedo.

When the Cubs touched up usually reliable reliever Zack Thompson for an unearned run in the 10th and kept the Cardinals off the scoreboard even with the heart of their order up, it led to another frustrating finish in a series for St. Louis. Oddly, the Cardinals are just 7-15 in series finales this season and they have dropped their past six. That has led to them either losing or splitting four of the past six series.

“We all wanted to win this game and we have to do a better job closing out the games,” said rookie catcher Iván Herrera, who had his first MLB hit with a single in the second inning. “This is a long journey, and everyone has to keep working.”

A large portion of St. Louis' hopes to make a deep playoff run center around Flaherty -- the Opening Day starter in 2020 and ’21 -- getting back to being the overpowering pitcher he’s been in the past. Those hopes took a hit in Spring Training when Flaherty showed up with lingering irritation in his shoulder. He and the team opted for a nonsurgical rehabilitation plan that involved a platelet-rich plasma injection, rest and strengthening exercises.

Flaherty performed well in rehabilitation starts at Double-A Springfield and Triple-A Memphis and wanted to make his next start at the MLB level. However, he has struggled with his control and mechanics in all three of his MLB outings. He allowed two first-inning runs against the Pirates and Brewers in his first two starts.

On Sunday, Flaherty pitched around a lead-off walk and a Goldschmidt error for a scoreless first inning. However, Flaherty struggled to get out of the second inning after allowing a double to Yan Gomes and throwing the ball into center field on a comebacker to the mound. The throwing error was Flaherty’s second in three games. After loading the bases, Flaherty got out of trouble in the second inning by striking out Christopher Morel and getting Rafael Ortega to ground out to second base.

“It sucks,” Wittgren said of Flaherty’s injury. “That guy worked his tail off to try and get back to the team and while trying to win games. We don’t know what happened, but hopefully he’s OK. We know how good he can be for us.”