Shelby Miller has followed the longest winning streak of his career with back-to-back losses, including an especially rough showing last week.
Danny Duffy is looking to rebound from a pair of ugly performances, too.
After going 6-0 with a 1.79 ERA over a seven-start stretch, Miller (6-4, 3.94 ERA) gave up four runs over five innings in a 5-3 loss at Cincinnati on May 23. The right-hander then surrendered a career-high seven runs over five innings of Wednesday's 7-4 defeat to the New York Yankees.
"It'll be hard to swallow, but then he's got to get back to work," manager Mike Matheny told MLB's official website. "He worked hard to get to a good spot and was getting positive results, as far as wins go, without having his good stuff. Right now is not the time to go to the drawing board and completely forget what he has been able to do."
Miller has gone 2-3 with a 6.99 ERA in six interleague starts since the beginning of last year. The only Royal with any experience against him is Norichika Aoki, who is 7 for 14 with a homer in their matchups.
Duffy (2-5, 3.57) is also looking to regain his form. The left-hander posted a 1.06 ERA in his first three starts after joining the rotation May 3, but he's since allowed 10 earned runs in as many innings while giving up four homers in his last two.
Duffy yielded six runs, seven hits and a season-high five walks in four-plus innings of a 9-3 loss to Houston on Wednesday.
"My velocity dipped pretty drastically compared to the prior start, but I think it's just something that all pitchers go through every now and then," he said. "The good ones pitch through it and get outs anyway, and I didn't. So depending on what I've got in the tank on Monday, I'm going to make better pitches. I can get outs no matter what and there are no excuses for giving it up like I did."
Duffy's only appearance against the Cardinals came as a rookie in 2011, when he allowed two runs and struck out a career-high nine over 3 2-3 innings of a 5-4 loss in St. Louis.
The Cardinals (30-27) have been outscored 30-15 during a 1-4 stretch, dropping three of four to San Francisco to close the week. Matt Carpenter stayed hot with two hits but the rest of the team went 2 for 28 in an 8-0 defeat Sunday.
"Losing is frustrating," said Carpenter, batting .390 during a 14-game hitting streak. "Anytime you lose a series to a team, whether they're playing well or not, is tough to swallow, especially at home.
"It happened, and now we've got to find a way to get better."
The Royals (26-30) had to settle for a split of a four-game set at Toronto, falling 12-2 on Saturday and 4-0 on Sunday. Jeremy Guthrie threw seven innings in the most recent game but Kansas City went 0 for 6 with runners in scoring position.
"The offense is definitely not living up to the capability it can live up to right now," said first baseman Eric Hosmer, mired in a 5-for-32 slump.
Hosmer is hitting .186 with no homers and four RBIs in 15 games versus St. Louis. Carpenter has recorded at least a hit in each of his seven games against Kansas City, going 11 for 30 with five extra-base hits.
The Royals are 1-6 in their last seven against the Cardinals. The teams play one more in St. Louis on Tuesday before shifting the series to Kauffman Stadium on Wednesday.