Scott Hartnell, Jason Arnott and Ryan Suter also scored for Nashville. Kristian Huselius scored twice and Daymond Langkow added a goal for Calgary, which had a five-game winning streak snapped.
Erat opened the scoring when he skated through the slot and fired a high shot that beat Miikka Kiprusoff at 14:41 of the first period.
Calgary tied it at 17:23 when Langkow skated from the right circle across the front of the net and shot from close range into the left side of the net as Nashville goalie Tomas Vokoun made a wrong move to the right.
With 22 seconds left in the first period, Huselius' close-in shot from the left side of the net slipped between the gap between Vokoun's leg pads.
During a second-period power play, Nashville's Jean-Pierre Dumont passed the puck from the right side of the net to the left. From there, Arnott poked the puck over Kiprusoff's outstretched leg as he was down on the ice at 15:59 to tie it 2-2.
Nashville scored two goals in an 80-second span to take a 4-2 lead.
Suter scored on a one-timer from above the right circle that beat Kiprusoff to his glove side at 2:28. Legwand doubled the Predators' advantage at 3:48 when he fired a shot high from the right side that got by Kiprusoff on the stick side.
Huselius scored his second goal of the game at 17:06 when he found the opening between Vokoun's pads with a wrist shot from the left circle.
Hartnell added an empty-net goal with 20 seconds left.
Notes: Nashville leads the NHL with 32 wins. ... The Predators are unbeaten against Calgary in eight games. Huselius is on a four-game point streak, tallying four goals and three assists. Arnott has six goals in seven games. Nashville's Paul Kariya had an assist to give him 11 points (four goals, seven assists) in eight games. Dumont was credited with an assist, extending his point streak to seven games (one goal, eight assists).