Morales' homer was his second in three at-bats, a span that started Tuesday night. He has four extra-base hits in three games, twice what he recorded in his first 15 games with the club since being acquired from Minnesota.
Iwakuma (11-6) failed to finish seven innings for the first time in eight starts, but the right-hander still struck out five without issuing a walk in 6 2-3 innings. It is the seventh time in that stretch Iwakuma has allowed two runs or fewer.
Three relievers bridged the gap to closer Fernando Rodney, who earned his 35th save in 38 chances. The Mariners won eight of nine on their homestand and remained tied with Detroit for the American League's second wild card.
The Blue Jays lost for the ninth time in 12 games to drop three games behind the final playoff berth.
R.A. Dickey (9-12) was shaky at times, but only allowed two runs and seven hits with four walks in six innings.
The Mariners threatened on numerous occasions to extend the lead, but Dickey was able to strand at least two runners three separate times. The third proved to be the veteran's greatest escape act, perhaps, as he avoided a one-out runners-on-the-corners situation by inducing a double-play grounder.
Mariners: OF Michael Saunders will return to Triple-A Tacoma to continue his rehab assignment after leaving the team to attend the birth of his second child, a son. Saunders, on the 15-day disabled list with a strained left oblique, will need more at-bats in the minors before rejoining the Mariners.
Blue Jays: 1B Edwin Encarnacion (strained right quadriceps) went 1 for 4 while playing all nine innings in the field on Wednesday for Triple-A Buffalo, which keeps him on track to rejoin the team on Friday in Chicago.
Mariners: Seattle looks to continue its strong play in Detroit on Friday as left-hander James Paxton, 5-0 in his career, makes the start.
Blue Jays: After a miserable start to an eight-game road swing, Toronto will get a day off before attempting to capture its first win of the trip against the White Sox.