Shields has faced the New York Yankees more than any opponent and will make his 29th start against them Sunday as these teams continue a four-game set in Kansas City.
The right-hander posted a 1.74 ERA during a three-start win streak May 7-18, but that figure has soared to 7.36 over his last three outings. Kansas City (30-32) has maintained its winning ways in those last three, with Shields (6-3, 3.68 ERA) failing to receive decisions.
His latest uneven performance came Tuesday in an 8-7 win at St. Louis, where he was charged with seven runs over 5 1-3 innings. Shields has allowed seven homers in his last 18 1-3 innings after yielding none over his previous 21.
His season-high four walks Tuesday were a surprise since he averages two per nine innings.
''I was just kind of all over the place, really wasn't commanding my slider at all,'' Shields said.
Shields is 8-15 with a 4.34 ERA in his career against the Yankees (31-30), going 1-1 with a 1.80 ERA in two starts against them in 2013 in his first season with Kansas City.
The player Shields has faced the most is Derek Jeter, who is a .294 hitter against him. That's the highest average of any Yankees hitter with more than five at-bats versus the Royals starter.
Struggling Mark Teixeira is hitting .180 with two extra-base hits in his last 15 games, and he's 6 for 48 with 15 strikeouts versus Shields.
Carlos Beltran is 0 for 5 against Shields and went 1 for 4 in Friday's 8-4 defeat. Beltran has been bothered by an ailing elbow and is still relegated to designated hitter duty.
''It's like starting over for me,'' Beltran said. ''One day, two days is not going to do it, any difference. Basically you have to play every day and with playing time that will come."
New York has not scored more than four runs in any of its last nine games.
''You've got to keep battling back,'' manager Joe Girardi said. ''We're still fighting.''
Hiroki Kuroda (4-3, 4.27) will start after allowing one run over 6 2-3 innings Tuesday in a 5-2, 10-inning loss to Oakland. The right-hander is 1-2 with a 3.63 ERA in three career outings against the Royals.
Kuroda has had trouble with Alex Gordon, who is 6 for 8 with two doubles against him.
Gordon is 8 for 17 during a six-game hitting streak and 2 for 5 with four runs scored in this series.
The Royals used two productive innings for the bulk of their scoring Saturday - a three-run second and a four-run sixth highlighted by Salvador Perez's three-run homer.
Eric Hosmer also went deep for Kansas City, which has won its last five games in which it has homered. The Royals are last in the majors with 28.
New York center fielder Jacoby Ellsbury is batting .396 during a 12-game hitting streak.
The Yankees, who won Friday's opener 4-2, are an AL-best 15-6 in day games.