Royal's return with 5:53 left in the contest came after the Broncos had tied the score 24-24 by outscoring the Raiders 17-7 during the third quarter.
Royal also hauled down a TD pass among his two catches for 25 yards and Willis McGahee returned from a broken hand to gain 163 yards with two scores on 20 carries for the Broncos (3-5).
Tim Tebow went 10-of-21 through the air for 124 yards and two touchdowns while also scrambling 12 times for 117 yards as Denver won for the second time in three games.
Carson Palmer made his first start as a Raider and connected on 19-of-35 passes for 332 yards and three touchdowns, but was also intercepted three times.
Oakland (4-4) got 129 all-purpose yards and a touchdown from Michael Bush.