Thornton scored 8:11 into the third period to tie the score at 2-2 and sent a puck on net from the left boards that Brent Burns deflected in for the winner with 3:59 remaining.
"I just saw Burnsie's big body in front and just threw it in there," said Thornton.
Mathieu Perreault and Teemu Selanne scored for the Ducks, who have struggled to a 2-4-2 record since winning their first two post-Olympic games. Frederik Andersen gave up three goals on 28 shots.
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