The fifth overall pick of the 2006 draft by the Seattle Mariners, Morrow beat his former team on Aug. 17 when he tossed six innings of three-hit, one-run ball with two walks and 12 strikeouts in a 5-1 triumph.
It was the ninth victory of the season for the 27-year-old Californian, putting him within one win of tying the personal high of 10 he established last season in 26 starts.
Morrow debuted with the Mariners in 2007 and was exclusively used in relief while going 3-2 with 18 holds in 60 appearances.
He started just 15 times in 71 outings over the next two seasons and won five games with 16 saves before being used as a full-time starter upon coming to Toronto.
He's 2-3 with a save, a hold and a blown save in eight meetings with the Royals.
Kansas City starts 34-year-old lefty Bruce Chen, who's won 21 games in 67 appearances across three seasons with the Royals - his 10th big-league team.
The 12 wins Chen recorded in 33 starts last season were his second-most in any year, trailing only a 13-10 performance with Baltimore in 2005.
Chen is 3-2 with a complete game in 12 appearances against the Blue Jays, including seven starts, with a 2.78 earned run average in 55 innings.
Kansas City is 5-5 in his last 10 starts.
Danny Duffy (3-8) suffered his fourth straight loss after giving up two runs on five hits in six innings, and the Royals fell to 4-13 in their last 17 games.
In Oakland, rookie left-hander Luis Perez one-hit the Athletics in six innings and Jose Bautista provided the offense with this 36th home run of the year to guide the Blue Jays to a 1-0 win in the finale of a four-game series.
Perez (3-2), who made 29 appearances out of the bullpen before getting his first chance to start, carried a perfect game into the sixth but gave up two walks and Oakland's only hit on a one-out single by Jemile Weeks.
He had four strikeouts and two walks and threw 50 of his 80 pitches for strikes to overshadow a good start by his counterpart.
Toronto has split four games with the Royals this season.