Morrow wobbled through four innings with only minimal damage, but then got rocked in the fifth as the Royals erupted for four runs and went on to a 6-3 victory over Seattle at Kauffman Stadium.
Nobody ever said that the reliever-to-starter transition is a smooth process and Morrow certainly felt the bumps while allowing six earned runs over four-plus innings.
"He just could not command his breaking ball at all," Riggleman said. "Overall, it was a step backwards. He has taken a couple of steps forward and one back, a couple forward and one back. We knew that was going to happen. We just have to bear with it. We knew it was possibly going to be a trying process."
The first four hitters in Kansas City's lineup jumped on Morrow with a succession of well-struck balls in the fifth to turn a 2-1 Royals lead into a cruise-control advantage of 6-1. In rapid-fire order, there was a leadoff homer by David DeJesus, a triple by Alberto Callaspo, a run-scoring single by Mike Aviles and a two-run homer to center by Ryan Shealy.
Just like that, Morrow was done for the night.
"It was a combination of not having command of his pitches and when he did get it in the strike zone, they were squaring him up pretty good," Riggleman said. "It was time to go."
Morrow said his mechanics were off and he simply couldn't make the necessary adjustments.
"[I was] really poor mechanically," Morrow said. "That's just one to forget."
Morrow recalled having a couple of games in Triple-A when his mechanics were also off.
"When you're relieving for one inning, you might be able to get through it," Morrow said. "But when you're trying to do it for five or six innings, it's going to catch up to you."
Riggleman had planned to use veteran left-hander Jarrod Washburn behind Morrow for a couple of days. There wasn't much good news on that front either as Washburn, pitching for the first time since Aug. 30 because of an abdominal strain, worked just one inning.
Washburn said he lobbied to pitch longer, but the Mariners noticed a change in Washburn's arm angle and Riggleman decided not to take a chance of having Washburn re-aggravate the abdominal muscle.
"They're right," Washburn said.
Asked if he felt he was done for the year, Washburn replied: "I'm guessing probably, yeah."
The Mariners fell to 0-6 on their 11-game road trip and are 57-93 overall. Seattle needs six wins in the final 12 games to avoid 100 losses.
"A guy like Raul [Ibanez] could look back and say 'I did all I could.' He has had an outstanding season," Washburn said. "There are a few other guys in that same situation. But as a team ... we had high expectations coming in and we've been brutal."
The Seattle offense again could not generate a sustained attack against Kansas City starter Brandon Duckworth. Jose Lopez again did his part with a 3-for-4 effort and a solo homer, but the remainder of the lineup managed just four hits.
The homer by Lopez in the fourth tied the game at 1, but the Royals quickly regained the lead on John Buck's RBI single. After Kansas City spurted ahead by five with the four-run rally in the fifth, the Mariners could manage only a couple of runs the rest of the way.
Jeremy Reed had a sacrifice fly in the sixth and the Mariners strung together hits by Lopez and Reed to begin the ninth. But that bid for a significant uprising fizzled quickly as All-Star closer Joakim Soria came on for his second save of the series.
The victory for Duckworth was the first of his career against the Mariners.
"He did a good job," Riggleman said. "He mixed his pitches and had us chasing some balls. Last night, their guy [Kyle Davies] went eight innings and tonight, their guy goes six. That really sets things up well for your bullpen."
Robert Falkoff is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.