With the match tied at four heading into the eighth end, Koe scored a single in the final end to seal his victory.
"It feels great," said Koe, who has now won two Grand Slam events after taking the 2012 Masters. "Obviously, when you make a big shot at the end to win, it feels even better and makes it more exciting."
The Calgary rink came out strong, putting up two points in the first end, but Gushue responded with two of his own to tie the game in the third.
Gushue took the lead with a single point in the fourth, and Koe responded with two in the sixth for a 4-3 edge before Gushue added one point in the seventh to tie it up.
Koe finishes the second event of the 2013-14 Grand Slam of Curling season with a 7-1 record, and takes home $24,000 of the combined $100,000 purse awarded to the 18 men's teams competing in the tournament.
Glenn Howard's rink from Coldwater, Ont., won the first Grand Slam event of the season — the Masters in Abbotsford, B.C., two weeks ago.