Matthew Liberatore was cruising through the first four innings on Wednesday night, needing just 46 pitches to keep the Athletics off the scoreboard. But baseball can change in a hurry, and for the young Cardinals left-hander, it all unraveled in a nightmare fifth inning.

After breezing through a seven-pitch first and a five-pitch third, Liberatore looked sharp and in control. He had pitched exceptionally in his previous two starts against the Dodgers and Padres, and the early signs were promising. Then came the fifth inning—and 43 pitches later, the game had slipped away.

The damage came off the bat of reigning American League Rookie of the Year Nick Kurtz, who crushed an opposite-field grand slam on a 2-2 slider down and away. It was the first grand slam of Liberatore's career, and it turned a tight ballgame into a 6-2 loss in West Sacramento.

"Kurtz took a really good swing on him—deep in the count and a slider kind of down and away, but he gets a really good swing on it," manager Oliver Marmol told Cardinals.TV. "He made us pay for it."

While the pitching staff struggled to contain the Athletics' bats, the Cardinals' offense had its own frustrations. Despite collecting 13 hits—including three from Alec Burleson and two apiece from JJ Wetherholt, Masyn Winn, and Nathan Church—St. Louis left runners on base in six of the first seven innings. They went just 1-for-9 with runners in scoring position and stranded 10 total baserunners.

Costly baserunning mistakes only added to the frustration. Winn was picked off third base, and Church was caught stealing, killing potential rallies. Marmol didn't hold back in his assessment.

"We did a lot of things that cost us, and I feel like this is one of the first games where I felt like we handed them the game instead of them beating us," Marmol said. "We had opportunities and we created a ton of them. But we didn't cash in, and we made some mistakes on the bases that cost us."

For Liberatore, the outing was a harsh reminder of how quickly momentum can shift in the big leagues. He allowed just five hits over four scoreless innings before the fifth-inning collapse, but five of the first six Athletics hitters reached base to start the frame. After walking Shea Langeliers to load the bases, Kurtz delivered the decisive blow.

The Cardinals will look to bounce back quickly, knowing that the margin for error is slim—especially when facing a lineup with as much firepower as the Athletics have shown this season.