Mendoza had his contract purchased Sunday from Class AAA Omaha, where he went 12-5 with a Pacific Coast League-best 2.18 earned run average. In two playoffs starts for the Storm Chasers, who won the PCL championship, he beat Round Rock and Sacramento and had a 1.29 ERA.
Mendoza will start Tuesday against the Tigers and Sept. 25 against the White Sox.
"He was the Pacific Coast League pitcher of the year; he deserves two starts," Royals manager Ned Yost said. "He deserves to come up here and, like (rookie Everett) Teaford, get a little bit of a head start going into next year."
Mendoza's previous major league start was Aug. 13, 2008 with the Rangers in a loss at Boston, giving up eight runs in four innings. In 36 games, including 14 starts, in the majors, Mendoza is 4-9 with an 8.43 ERA with opponents hitting .333 off him.
The Royals acquired Mendoza for cash considerations on April 2, 2010. He was in the Kansas City bullpen at the beginning of last season, but was designated for assignment April 22 after allowing 10 runs on 10 hits, including four home runs, in four innings in four appearances.