Lowry opened the scoring, putting the IceCaps ahead on a backhander five-hole in front of the net at the 5:09 mark of the first period.
Albert added to the lead 12:21 into the first, cleaning up a Jason Jaffray rebound on the power play.
Thirty seconds later, Mouillierat put the IceCaps up 3-0, finishing off a pass out front, beating Lawson high.
Mouillierat added his second of the game with a high wrister 10:18 into the second, from the right faceoff dot on the power play.
Albert added his second of the game, stripping a defender of the puck and scoring on a breakaway after a quick backhand-to-forehand move with 31 seconds left in the second period.
O'Dell added insult to injury, scoring a penalty shot with a quick shot to fool Lawson 2:38 into the third.
Robinson put the Senators on the scoreboard with a high blocker wristshot at the 7:53 mark of the third.
Pageau added another for the Senators, finishing a cross-crease tap-in 10:14 into the third.
St. John's went 2-for-9 on the power play, while the Senators were 1-for-5 with the man advantage.