Gil Meche, the Royals' No. 1 starter, departed in the fifth inning after giving up seven runs on 11 hits. Felix Hernandez, Seattle's starting pitcher, left in the sixth with the same ailment after having much better luck.
Hernandez and the Mariners prevailed in a 10-2 pounding of Meche and the Royals as 28,651 fans observed the batting, fielding and medical proceedings at Kauffman Stadium.
For the Royals, after a giddy spurt of eight wins in 10 games, this was a second straight shellacking. They lost to the Cleveland Indians, 10-3, on Thursday night.
"Two days ago we had it rolling and now we've taken a step back, but the beauty of it is we get a chance to try again tomorrow," first baseman Ryan Shealy said in a quiet Royals clubhouse.
On another optimistic note, Meche said that he's had this achy back thing before and has overcome it.
"I'll be fine in two days, for my bullpen," he assured reporters.
Meche felt his lower back pull in the second inning when he was pitching to Jose Vidro, but didn't tell anyone.
"We didn't know anything about it until he came out [of the game]," Royals manager Buddy Bell said.
Bell noted, though, that Meche's pitches crept upward and became hittable. More hittable, anyway.
Even before the back ache, the Mariners' Ichiro Suzuki pounded Meche's second pitch of the game over the right-field fence. The leadoff homer gave Ichiro an 18-game hitting streak during which his average is a scorching .443 (35-for-79).
"The first pitch was a ball," Meche said. "The second pitch got into a kind of danger zone."
Finally, after the homer, five doubles and five singles, Meche had let in seven runs and was getting uncomfortable. Assistant trainer Frank Kyte arrived to escort him off the field.
"I felt my legs were a little off where I just couldn't push off and let the ball go," Meche said.
Zack Greinke took over and got two quick outs, but his string of five consecutive scoreless relief outings ended in the sixth. The inning began with a Vidro triple, Jose Guillen's double, Raul Ibanez's double and Richie Sexson's single.
David Riske, though, worked 1 2/3 scoreless innings and Octavio Dotel added 1 1/3 as he labors his way back from an injury.
Hernandez, who threw a one-hitter early this season and then went on the disabled list, proved to be a puzzle. He shut out the Royals for five innings, finally yielding to his own ailing back after Shane Costa's run-scoring triple and Alex Gordon's RBI double.
Before that, the Royals were looking up at a 10-0 score.
"You get down 5-0 or 6-0 and the game really changes," Bell said. "You've got to outhit them and with a guy like that, it's tough to do."
For his part, Hernandez vowed he wouldn't miss his next start.
Costa, before his triple, struck out twice against Hernandez.
"He has a good live fastball and a 91-mph slider," Costa said. "It doesn't get much better than that."
Or worse, if you're a Royals fan who was revved up by the 8-2 winning surge. Two lopsided losses and then your top starter's back goes balky, too.
"I just feels like your whole backside dies," Meche said. "I've had this almost every year but I've been able to get through it."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.