He gave up hits to the first three batters he faced and the Mariners built an early lead they wouldn't relinquish in a 4-3 victory over Toronto in front of a season-low Rogers Centre crowd of 12,935.
Morrow tied a career high by giving up 11 hits over four-plus innings as the Blue Jays had their four-game winning streak come to an end. Toronto (64-76) had its chances against Seattle starter Erasmo Ramirez (1-2) but couldn't put together a big inning.
Morrow needed 27 pitches to get out of the opening frame. The Mariners put up two early runs and were on their way to ending a three-game skid.
"I think the only thing that kept that from being eight runs was probably my change-up," Morrow said. "I had a decent change-up and was able to keep them off-balance a little bit that way.
"But it was just one of those days, really."
Seattle (68-74) had four of its 14 hits in the opening frame. Morrow had given his former team fits in the past, winning all three of his starts and posting an impressive 1.89 earned-run average.
The Mariners used a balanced offensive attack with all but one starter recording at least one hit. Kyle Seager was a triple short of the cycle and Franklin Gutierrez added two hits and a run.
"We were ready for the fastball," Gutierrez said. "(Morrow) is a power pitcher and obviously we need to get on the fastball first and that's what we did, get him early and try to score some runs early in the game."
Ramirez pitched seven effective innings for his first major-league win. The Blue Jays put the tying run in scoring position in the ninth before Tom Wilhelmsen picked up his 25th save by getting Anthony Gose to ground out to end it.
Morrow had made three solid starts since returning to the lineup after a stint of over two months on the disabled list with an oblique injury. He said he felt fine physically and gave credit to the Mariners' offence.
"They did a good job of putting the bat on the ball there in (the first) inning," he said. "Then the whole time I just kind of felt out of sync with my body. I couldn't really find my release point.
"I was just struggling in that regard."
Morrow allowed four earned runs and had four strikeouts with a walk. He threw 63-of-93 pitches for strikes.
"He wasn't as powerful, wasn't as sharp," Jays manager John Farrell said. "It was a little bit more difficult for him tonight to command the bottom of the strike zone.
"Early on in the first inning, the two runs on four hits, there were some fastballs that were up out over the plate and they did a good job of going the other way with them."
Leadoff man Dustin Ackley doubled to start the game and moved to third on a Gutierrez single. Seager singled to bring Ackley across with the game's first run.
After a force out and a walk, Michael Saunders of Victoria lashed a single to left that allowed Gutierrez to score easily. Jaso tested the arm of Rajai Davis on the play but the Jays' left-fielder fired a perfect throw to catcher J.P. Arencibia for the out.
The Blue Jays answered with a run in the bottom half of the frame.
Colby Rasmus reached on an infield single and Adam Lind's flare to shallow left dropped in for a hit. Yunel Escobar hit a two-out single that scored Rasmus but Lind was thrown out at third base to end the inning.
Both teams added singles runs in the third inning.
Seager hit a one-out double, moved to third on a wild pitch and scored when Jaso hit a hot shot that was too much for Jays second baseman Kelly Johnson to handle. Davis later picked up his second assist of the game by throwing out Jaso at third base.
In the bottom half, Gose singled and moved to third on a single by Brett Lawrie of Langley, B.C. Gose scored easily when Rasmus hit a sacrifice fly to right field.
Escobar doubled to lead off the fourth inning but Ramirez got a strikeout, fly out and grounder to preserve the one-run lead.
Seattle put runners on the corners with one out in the sixth but reliever Brett Cecil got out of the jam when Gutierrez grounded into a double play. Toronto stranded two runners in the seventh inning when Lawrie flew out to centre field.
The Blue Jays made it a one-run game in the eighth inning. Rasmus hit a ground-rule double, moved to third on a sacrifice fly from Edwin Encarnacion and scored when pinch-hitter Moises Sierra hit a high chopper to second base.
Toronto had eight hits on the night.
Notes: On-field tributes were held around the major leagues Tuesday on the 11th anniversary of the 9/11 attacks. Ballcaps had American flag patches embroidered on the side with the Blue Jays adding the Maple Leaf on the other side. Damien Walsh sang the national anthems and Len Stadler — also with Toronto Fire Services — threw out the ceremonial first pitch. ... Gutierrez committed a rare error in the seventh inning when he dropped a fly ball in centre field. That ended his American League-record streak of consecutive errorless chances by an outfielder at 846. Darren Lewis holds the major league record (938). ...The game was the opener of a six-game road trip for the Mariners. ... The Blue Jays have a 189-170 edge in all-time meetings with their expansion cousins. ... Seattle right-fielder Eric Thames returned to Toronto for the first time since the Jays traded him to the Mariners on July 30. He was 0 for 4 with three strikeouts. ... Left-hander Ricky Romero (8-13) is scheduled to start for the Jays on Wednesday night against right-hander Kevin Millwood (5-12). ... Right-handers Felix Hernandez (13-7) and Henderson Alvarez (8-12) are the scheduled starters for the finale of the three-game set on Thursday night.