Austin Carroll and Ben Walker each scored and added an assist for the Royals (30-19-4).
Connor Sanvido had the Thunderbirds' only goal (19-31-5).
Victoria opened the scoring on the power play when Brandon Magee fed Carroll in the slot for a quick snapshot that beat Seattle goalie Brandon Glover low glove side.
Walker made it 2-0 halfway through the first period after taking a perfect feed from Carroll and scoring on a low wrist shot from just inside the right face off circle.
The Royals extended their lead to three goals on another power-play goal when Crooks picked up a loose puck in the goalmouth and poked it behind a fallen Glover.
The Thunderbirds got on the scoreboard early in the second period on a quick backhander from the slot by Sanvido.
The Royals made it 4-1 when Crooks scored his second of the game, breaking past the Thunderbirds defence and sliding the puck past goalie Danny Mumaugh, who had relieved Glover at the start of the second.
Royals goalie Patrick Polivka made a number of big saves during the game and shut the door in the third period, making eight saves.
Polivka continued his hot streak, stopping 31-of-32 shots in the game for his 26th win of the season. Glover made eight saves on 11 shots before being pulled in favour of Mumaugh, who stopped 18 of 19.