CINCINNATI -- Steven Matz was so good on Saturday, so downright electrifying with a two-seam fastball that touched 96 mph several times, that it made the disappointment of his knee strain hurt even more to a Cardinals squad counting on a healthy stretch from the talented left-hander.

In the midst of an otherwise brilliant first start since coming back from a shoulder injury that shelved him for two months, Matz and the Cardinals saw disaster strike when the lefty strained his left knee bobbling a slow roller toward the first-base bag. Matz, who signed a four-year, $44 million free agent deal last fall, will undergo an MRI on his knee on Sunday to determine how much time he will have to miss with the injury -- if any. But another stint on the injured list is almost certain now.

• Box score

“It feels OK,” Matz said to Bally Sports Midwest. “Hopefully it’s just a little sore and I won’t miss any time -- that’s the best-case scenario.“

Pitching for the first time at the MLB level since May 22 when he left after four pitches with shoulder discomfort, Matz struck out seven batters -- including five in a row before the ground ball that ended his night -- in the Cardinals 6-3 victory over the Reds at Great American Ball Park. He allowed three hits and two earned runs in 5 1/3 innings of work and was likely coming out of the game after hitting the 90-pitch mark just before his injury.

• Cardinals Injuries & Moves

Reds slugger Joey Votto hit a slow roller to the right side, and in Matz’s haste to field the ball, it hit off his glove. As his foot slid in the dirt, he felt his knee hyperextend. The uncertainty surrounding the injury marred an otherwise stellar effort from the left-hander, who improved to 4-3 in his first season with the Cardinals.

“[It was] an easy ground ball that I should have caught -- that’s the first problem,” Matz said. “Then, I went to reach out and overextended my knee a little bit.

“I felt really good -- that’s what’s so frustrating because that’s probably the best I’ve felt all year. I didn’t get tired, and I was feeling stronger as the game was going on. So I’m happy with that.”

Matz needed two cortisone injections and four Minor League starts over the past two months to get himself ready for an MLB return. His scheduled start last Sunday was rained out, so he threw an 81-pitch bullpen in St. Louis instead to ready himself for Saturday’s start in Cincinnati. On Saturday, he recorded five of his first six outs on changeups, touched 96 on the radar gun several times and overpowered the Reds as the game wore on.

“On that two-seamer, he had a 57 percent whiff rate, which is really, really good,” Cardinals manager Oliver Marmol said. “The two-seamer was a big player for him.”

Marmol wasn’t happy about seeing Matz go down, especially because the organization needs balance to their righty-heavy rotation.

Cardinals first baseman Paul Goldschmidt, who hit his 22nd home run of the season and earlier drove in his 1,000th career run, said he wishes he had called Matz off of the ground ball and taken the play himself.

“Hopefully he’s OK, but I haven’t heard anything,” said Goldschmidt, who became the 118th player in MLB history with at least 300 home runs, 1,000 runs and 1,000 RBIs -- all milestones hit this season. “He pitched really well, especially closing out those last few innings, and hopefully he’ll be back as soon as possible.”

On Saturday, Matz got swings and misses on 12 of the 21 two-seam fastballs he threw. That two-seamer, which replicates a sinker with its downward movement, topped out at 96.5 mph -- up quite a bit from his season average of 94.4 mph. Marmol said the latest injury is especially frustrating because the left-hander showed how good he can be when healthy.

“That’s the reason we got him -- what he showed today is exactly it,” Marmol said. “His ability to get punchouts -- six with the two-seamer -- that’s why we signed him. It’s unfortunate that on the last hitter he was going to face, he went down.”