The White Sox braced themselves for a sixth-inning drop-off from Javier Vazquez.
But they didn't envision a defensive letdown or a failure to solve Runelvys Hernandez.
Those shortcomings haunted them Tuesday night in a baffling 4-2 loss to last-place Kansas City that dropped them 6½ games behind first-place Detroit in the American League Central and ended their five-game winning streak.
The Sox (71-47) also had their AL wild-card lead cut to two games over Minnesota.
The Royals snapped a five-game losing streak and a 2-2 tie on Mark Teahen's two-run home run off Vazquez in the sixth, but the Sox's problems surfaced much earlier.
Jermaine Dye's dropped fly ball in right with two outs allowed the Royals to add a run for a 2-0 lead in the fifth. And the Sox's run output was their lowest since a 3-1 loss to Texas on July 22.
With the exception of the fifth inning, the Sox failed to get a timely hit off Hernandez, who entered with an 8.15 ERA and failed to pitch at least five innings in his two previous starts against the Sox this season.
Instead, Hernandez (3-7) went 72/3 innings and won for the first time in five starts.
Vazquez (11-7), meanwhile, continues to baffle the Sox with his middle-inning woes. He jumped in front of the mound in frustration after Teahen's drive carried over the fence.
Opponents now are batting .361 after the second time around in the order against Vazquez, who fell to 4-1 lifetime against Kansas City.
"I felt like I didn't have the command I usually have," said Vazquez, who failed to earn more than one strikeout in a start for the first time since Aug. 31, 2004, against Cleveland. "I was falling behind and missing spots. The positive thing I can take out of this is that the game didn't get out of hand."
The Sox's uphill night started after Scott Podsednik led off the bottom of the first with a double only to be left stranded by the middle of the Sox order.
Rallies in the third and fourth were halted by double plays by Jim Thome and Dye, who had his 12-game hitting streak snapped.
The Sox finally broke through in the fifth. Juan Uribe started the rally with a one-out single and Brian Anderson followed with a drive down the left-field line that a fan touched for a ground-rule double.
Uribe scored on Podsednik's sacrifice fly to center and Tadahito Iguchi ripped a 1-2 pitch up the middle for a game-tying single. Thome followed with a double down the right-field line.
Even with cleanup hitter Paul Konerko in the on-deck circle, third-base coach Joey Cora constantly waved Iguchi toward home. But second baseman Mark Grudzielanek's accurate one-hop throw arrived early enough to nail Iguchi for the final out.
"With two outs, you have to take a chance," Guillen said in defense of Cora.
That merely set up more frustration. Grudzielanek led off the sixth with a single and Teahen followed with a two-run, tie-breaking homer to center. The homer snapped Teahen's 0-for-10 slump, but he has three homers and nine RBIs against the Sox this season.
Before Guillen could pull Vazquez, Brown and Sanders hit consecutive one-out singles. "We just didn't hit well, but Javy did a good job," Guillen said.
David Riske threw 2 2/3 scoreless innings of relief, his longest outing since joining the Sox on July 16. The Sox's bullpen has a 1.84 ERA over its past 11 games.
Royals 4, White Sox 2