It was the first time since August 1, 2009, that Hernandez allowed more than three runs over at least six innings. The streak was the longest in franchise history, breaking the mark of 14 set by right-hander Erik Hanson in 1991.
"It was not my day today," Hernandez said. "My pitching was all right, but it was not my day."
Hernandez said that his back tightened up during the start and reached the point where he received treatment between innings.
"I'm the kind of guy, I don't like to say nothing," he said. "I'm going to go out there and just battle.
Hernandez assured everyone that his back would be fine and he'll make his next start, scheduled for Friday night against the Angels at Safeco.
"I'll be ready for the next one, that's all."
Rob Johnson, who caught Hernandez on Saturday, said that the right-hander's impairment was obvious.
"He just didn't have the finish on pitches that he normally has," Johnson said. "Usually, within the last five to ten feet, his stuff is moving in every direction. He didn't have that today."
Hernandez's streak was the third-longest in the Major Leagues since 2000. Only Chris Carpenter of the Cardinals, who had 22 in 2005, and Johan Santana, 21 for the Twins in '04, had longer streaks of surrendering three or fewer runs in six innings.
Hernandez was lifted for reliever Jesus Colome in the fifth inning against the Rangers after he surrendered a solo home run to Josh Hamilton and back-to-back walks.
Manager Don Wakamatsu said that he could see Hernandez struggling to control his pitches, but he didn't believe the injury to be serious.
"You are watching him out there, and his command wasn't there," he said. "His changeup wasn't quite as sharp. He walked around, taking more time out there, but about the third or fourth inning, he had to come in and have it adjusted. At that point, we knew he wasn't right."
The second and third runs were scored with two outs in the second inning, when a seemingly catchable ball fell untouched between left fielder Milton Bradley and center fielder Franklin Gutierrez.
Hernandez, the staff ace and runner-up to Royals right-hander Zack Greinke in the Cy Young Award race last season, saw his personal nine-game winning streak end in his previous start.
Jim Street is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.