KANSAS CITY, Mo. As he walked off the Kauffman Stadium pitcher's mound Sunday afternoon, Johnny Cueto pulled his leather glove to his face and screamed into its dark webbing. Here was a struggling pitcher, disgusted and dismayed, already covered in sweat as he sunk deeper into the most vexing stretch of his sterling career.

It still was the first inning of an eventual 7-5 loss to the Chicago White Sox. Cueto already had surrendered three runs and four base runners. His fastball lacked consistent command. His off-speed arsenal was ambushed by a lineup of eager hitters. For the fourth straight start, Cueto toed the combustible line between human and ineffective.

As Cueto screamed into his glove and returned to the dugout, a handful of disgruntled shouts and boos cut through a wave of cheers.

"He's just going through a stretch right now," Royals manager Ned Yost said. "You kind of liken it to a hitter that goes into a slump."

In terms broad and specific, Cueto does not know what is wrong. His arm feels healthy, he says, his body strong. He feels like the same pitcher that shredded hitters in the National League for eight seasons as the ace of the Cincinnati Reds. But for more than two weeks -- 20 innings over four subpar starts -- Cueto has not been that pitcher. For a club with World Series aspirations, the Cueto problem looms over the Royals' September and their postseason chances.

"We're not worried about it," teammate Eric Hosmer said.

"He's a veteran guy," Jarrod Dyson said.

"He's not frustrated at all," said Royals catching coach Pedro Grifol, who translated for Cueto. "He's just a little bit disappointed that he hasn't been able to help the team the way he's supposed to help this club."

On Sunday, Cueto lasted just three innings, coughing up five runs and seven hits and continuing a weekend of forgettable starting pitching from the Royals staff. On Friday, the White Sox battered right-hander Kris Medlen. On Saturday, Danny Duffy was done in by a couple costly misses. On Sunday, Cueto could not shake the ineffectiveness that has confounded him since late August. Yost pulled him after just 77 pitches.

"He's just grinding through it right now, without any results," Yost said. "But these things turn around quick, especially with a pitcher of Johnny's caliber."

The Royals (82-54) were swept in a three-game series for the first time since losing three straight to the Astros in Houston June 28-30. Their lead over the Toronto Blue Jays for the American League's best record is now down to four games. Kansas City on Monday will begin a three-game home set against the Minnesota Twins.

For the moment, the Royals' cushion in the AL Central is an enviable 12 games, but the concerns over Cueto will grow more palpable as October approaches.

Sunday marked six weeks to the day since the Royals' front office acquired Cueto from the Cincinnati Reds in exchange for left-handers Brandon Finnegan, John Lamb and Cody Reed. The strategy behind the swap was simple and straightforward. The Royals were barreling toward the postseason for the second straight year, and in Cueto, the Reds' ace, they had a front-line horse to ride in October.

To this point, the returns have been less than satisfactory. After three sterling starts in early August -- including a shutout against the Detroit Tigers on Aug. 10 -- Cueto has lost four straight starts. The numbers are even worse: In 20 innings over four outings, Cueto has been mauled for 21 earned runs and 37 hits.

On Sunday, Yost said the problem was not mechanical. Cueto has been working with pitching coach Dave Eiland, trying to shore up a problem in which his front side flies open and his off-speed pitches stay flat. That, according to Yost and Cueto, did not appear to be the issue against the White Sox.

"He's going to look at video," Grifol said, translating for Cueto. "He's going to continue to work. (This is) the first time he's had a streak like this, but he's going to go out and do what he does and continue to work in between starts."

While Cueto struggled early, and reliever Chris Young surrendered a solo homer in the sixth, the Royals remained within striking distance of Chicago thanks to a trio of solo homers. Salvador Perez drilled a solo shot to right in the second, his 19th homer of the year. Dyson and Mike Moustakas clubbed homers off White Sox starter Erik Johnson in the sixth.

The Royals continued the comeback in the seventh, manufacturing two runs on two hits and a hit batter. White Sox reliever Jake Petricka began the inning by beaning Perez. Paulo Orlando followed by cracking a double to left. And the runs scored on an infield single from Dyson and a sacrifice fly from Alcides Escobar. The rally cut the White Sox's lead to 6-5, but the offense stalled against Chicago reliever Zach Duke, who struck out the side in the eighth while flummoxing Moustakas, Kendrys Morales and Alex Gordon.

The Kansas City offense was working shorthanded on Sunday. Yost offered days off to Hosmer -- who pinch-hit in the seventh -- and center fielder Lorenzo Cain. Gordon served as the designated hitter, while Morales played first base. Dyson subbed in center field.

The bats still provided five runs, enough offense to secure a victory against a Chicago club that has spent most of the year under .500, but the Royals could not escape the hole dug by Cueto, who dropped to 2-5 with a 4.86 ERA in eight starts with Kansas City.

"It takes a little while for guys to settle in and get comfortable with the league and make your adjustments," Hosmer said. "It's a guy -- he's been pitching in the National League for a long time, and he's still trying to adjust to the hitters and adjust to his style of pitching."

Standing in front of his locker on Sunday afternoon, Cueto could not offer a diagnosis for his struggles. This is new to him, too, he said. But he vowed to hit the video room, to study his latest outing, to try to figure out what's wrong.

"He actually feels stronger," Grifol said. "He's just got to go look at it and see if he finds something."