The Tigers enter the season's final two weeks having already clinched the American League's Central Division title - their first division championship since winning the AL East in 1987.
Detroit reached the World Series as a wild card in 2006 after finishing second in the Central.
Penny, a 33-year-old righty, was 3-4 in nine starts with St. Louis last season and had won 20 games in the majors in three seasons since going 16-4 with the Los Angeles Dodgers in 2007.
He's won 10 of 20 decisions in his first year as a Tiger, however, including an 8-4 verdict over Minnesota on Sept. 9 in which he allowed four runs on five hits in eight innings.
One subsequent start, at the Chicago White Sox five days later, yielded a no- decision in Detroit's 6-5 win.
In three career starts against the Royals, Penny is 1-1 with a 2.70 earned run average in 20 innings.
Hell be faced by journeyman right-hander Luis Mendoza, who makes his first appearance of 2011 and 37th in a career that began when he debuted with Texas in 2007.
A 27-year-old native of Mexico, Mendoza was 1-0 in six games with the Rangers as a rookie, then went 3-8 across 25 appearances - 11 starts - a season later with an 8.67 earned run average in 63 1/3 innings.
He appeared in one game and pitched two innings with Texas in 2009, then made four appearances with the Royals last season while allowing 10 runs in four innings.
The 6-foot-3, 235-pounder has made 33 appearances this season at Triple-A Omaha and is 12-5 with a 2.18 ERA in 144 1/3 innings.
He is 0-1 lifetime against Detroit in six games with a 15.12 ERA.
On Sunday in Oakland, Justin Verlander padded his potential Cy Young Award- winning season -- and MVP candidacy -- with another sublime outing, tossing eight scoreless innings in the Tigers' 3-0 victory over the Athletics.
Verlander (24-5) won his club-record 12th consecutive start by yielding just three hits and three walks, while also becoming the first American League pitcher to notch 24 wins since Oakland's Bob Welch won 27 in 1990.
Austin Jackson went 2-for-5 with a solo homer.
In Kansas City, A.J. Pierzynski finished 4-for-5 with a pair of home runs and four RBI to lead the White Sox to a 10-5 victory over the Royals in the finale of a four-game series.
Eric Hosmer went 3-for-5 with an RBI and run scored, while Johnny Giavotella picked up three hits including an RBI triple for the Royals, who had their season-best seven-game winning streak ended.
Bruce Chen (11-8) was tagged with the loss after giving up four runs on nine hits in 5 1/3 innings. He struck out two and walked two.
Detroit is 10-6 against the Royals this season.