The St. Louis Cardinals' search for better starting pitching will continue Saturday when they host the Cincinnati Reds.

The Cardinals have gone from deploying a six-man starting rotation to scrambling to fill five spots. Manager Mike Shildt held off on announcing Johan Oviedo his starter for Saturday's game until after Friday's 6-4 loss to the Reds.

Cardinals ace Jack Flaherty could miss several weeks with his oblique muscle strain. Veteran Miles Mikolas is sidelined until at least August with a setback to his surgically repaired flexor tendon.

Kwang Hyun Kim exited Friday night's game after three innings with lower-back tightness, which is the same issue that sidelined him earlier this season.

Carlos Martinez retired just two batters while allowing 10 runs Wednesday. All of this has put extra stress on the beleaguered Cardinals relievers.

"We've had some situations with our starters in two of the last three games," Shildt said. "The bullpen has had to carry the mail."

Oviedo (0-2, 5.40 ERA) started this season on a good note, throwing 4 2/3 scoreless innings in mop-up relief against the Milwaukee Brewers on April 11.

But he has struggled mightily as a fill-in starter, posting a 7.04 ERA in his four outings. In 15 1/3 innings, he allowed 13 runs (12 earned) on 15 hits, 13 walks and two hit batters.

The Reds won the first two games in this four-game series at Busch Stadium. They have won four of their last five games overall while the Cardinals have lost five of their last six games.

"I'm a big believer in habits," Shildt said. "I'm a big believer in habits winning over a period of time. You've got a group of guys that are going to scratch, fight, claw for everything they get all the time and are talented. You can live with that. You know you are getting the most out of your club."

Reds starter Tyler Mahle (4-2, 3.42) will try to extend his scoreless stretch Saturday after throwing 10 1/3 shutout innings in his last two starts.

Mahle struck out 10 batters, walked two and allowed just four hits in those games -- a 2-1 victory over the Washington Nationals and 5-1 over the Chicago Cubs.

"He's just so tough and he's so strong," Reds manager David Bell said. "Tyler finds an extra gear, reserve in the tank and he's able to get big outs. We'll take that every time. Tyler continues to get better."

Mahle earned a 9-6 victory over the Cardinals on April 3 while allowing three runs (two earned) on four hits in five innings. Paul DeJong hit two homers off him in that game, but he is on the 10-day injured list with cracked ribs.

In nine career starts against the Cardinals, Mahle is 2-3 with a 5.24 ERA. Aside from DeJong, Yadier Molina (9-for-19, two homers, five RBIs) and Paul Goldschmidt (5-for-15, double, three walks, RBI) have done damage against him.

But Tommy Edman (1-for-11), Matt Carpenter (2-for-17, seven strikeouts) and Nolan Arenado (1-for-8) have struggled against him.

On the injury front, Reds first baseman Alex Blandino exited Friday night's game after being hit in the right wrist with a pitch.