De Vries (4-5) has four career victories and three of them are against the Royals. He limited the Royals to one run on seven hits, walked none and struck out three over 6 2/3 innings. De Vries has won back-to-back starts, holding Texas and Kansas City to 10 hits and two earned runs in 11 2/3 innings.
Morneau, who has 77 career RBIs against the Royals, doubled home Josh Willingham in the first inning with the first Twins' run.
Royals rookie Will Smith (4-7) lost his third consecutive start, giving up three runs on nine hits and two walks, while striking out four in six-plus innings.
The Twins loaded the bases with one out in the seventh, but reliever Vin Mazzaro got out of the jam when Doumit grounded into a double play after Morneau was intentionally walked. Mazzaro had not pitched since Aug. 21 in the minors.
Glen Perkins worked the ninth for his ninth save in 12 opportunities.
Royals right fielder Jeff Francoeur logged his major league-leading 16th assist in the fifth when he threw out Willingham trying to go from first to third.
Manager Ron Gardenhire said the Twins "might go" to a six-man rotation with the additions Saturday of RHPs P.J. Walters, who was reinstated from the disabled list, and Esmerling Vasquez, who was promoted from Triple-A Rochester and is scheduled to start Sunday against the Royals. Vasquez was strictly a reliever from 2009-11 with Arizona, but the Twins plan to look at him as a starter. Walters started before shoulder inflammation shut him down for 70 games. .There were 6.54 inches of rain to fall at Kauffman Stadium in a 29-hour period before the first pitch Saturday, which was delayed 21 minutes. .The Royals recalled OF David Lough, who hit .275 with Triple-A Omaha, and C Manny Pina, who hit .260 in 43 games with Triple-A Northwest Arkansas after having right knee surgery in spring training. .The Royals dropped to 7-22 against the Twins, Seattle and Toronto, the three last-place teams in their AL divisions.