With the win, the league-leading Winterhawks (46-8-3) increased their lead atop the Western Division to eight points over the idle Edmonton Oil Kings.
Carter Popoff opened the scoring for the league-worst Giants (14-42-0) on Vancouver's first shot on goal nine minutes into the game.
It didn't take long for Portland to re-establish control with Brendan Leipsic tying the game 10 seconds later with his 40th goal of the season. Leipsic also had three assists. Goals by Chase De Leo, Rattie and Keegan Iverson made it 4-1 Winterhawks after one period.
The Giants showed some pushback early in the second period with goals by Jackson Houck and Jason Trott in a 42-second span, before Rattie scored his second of the game on a power play, and Josh Hanson's first of the season to make it 6-3 Portland.
Rattie added two more goals in the third period, giving him 35 for the season.
Brendan Burke, the 17-year-old son of former NHL goaltender Sean Burke, made 35 stops for the Winterhawks.
Payton Lee, one of five 16-year-olds in the Giants' lineup, was pulled by coach Don Hay after Hanson scored to make it 6-3 at the 10:06 mark of the second period. Jared Rathjen allowed just two goals the rest of the way.
There were just three penalties in the game, with Portland going 1 for 2, and Vancouver coming up empty on its lone man advantage.