Lewis picked off starting Raiders quarterback Kyle Boller less than 4 minutes into the game and ran 59 yards for a touchdown. Flowers capped the scoring with a 58-yard return off a Carson Palmer pass in the fourth quarter.
In between, the Chiefs logged four more interceptions for a total of six -- three off Boller and three more off Palmer, who made his Raiders debut after being obtained from Cincinnati in a trade last week.
Matt Cassel completed 15-of-30 passes for 161 yards and was intercepted twice himself for the Chiefs (3-3), who notched their third straight win after an 0-3 start.
Palmer completed 8-of-21 pass attempt for 116 yards for the Raiders (4-3).