The 26-year-old has won five consecutive starts since mid-July to improve his season record to 12-9, just two shy of the career-high 14 victories he posted across 32 starts in 2010.
Romero was a 13-game winner as a rookie in 2009 in 29 starts.
He notched win No. 12 in start No. 25 this year, scattering three hits and striking out six in nine scoreless innings while beating Oakland, 7-0, on Aug. 18.
It was the seventh complete game and third shutout in 86 career starts for Romero, who has split two lifetime decisions with the Royals.
Kansas City broke out on top of the series on Tuesday night, when Bruce Chen pitched 7 2/3 strong innings to guide the Royals to a 6-4 victory.
Chen (9-5), a journeyman who has pitched for 10 teams in his major league career, gave up three runs on four hits. He fanned a season-high nine batters and issued only one walk. Joakim Soria gave up a run in the ninth, but recovered to record his 23rd save of the season.
Billy Butler and Eric Hosmer cracked home runs, while Johnny Giavotella added an RBI double and Salvador Perez added two RBI for the Royals, who had lost three of four to the Boston Red Sox over the weekend.
The Royals send former No. 1 overall draft pick Luke Hochevar to the mound with hopes of ending a three-start drought.
The top pick in 2006 out of the University of Tennessee leveled his 2011 record at 8-8 with a 6-2 defeat of Baltimore on Aug. 3, but has since allowed 21 hits and 10 runs in 19 innings while getting a no-decision at Tampa Bay and losing to the Chicago White Sox and Boston.
He is 3-1 in four starts against Toronto with a 3.16 earned run average in 25 2/3 innings.
Kansas City is 7-3 in his last 10 starts.