Koe (1-0), who shot 86 per cent, scored four in the sixth to seal the victory at Mattamy Athletic Centre. He had deuces in each of the second and fourth ends.
Gushue (0-1) shot just 66 per cent and scored singles in the first and fifth ends.
The Players' Championship is the last of five events on the Grand Slam of Curling schedule. The tournament runs until Sunday.
In other first-draw men's play, Winnipeg's Mike McEwen (1-0) put up single points in the final two ends to edge Sven Michel of Switzerland 7-5.
On the women's side, Ottawa's Rachel Homan is also 1-0 after a convincing 10-3 win over Sweden's Margaretha Sigfridsson.
Homan shot 94 per cent, scoring three in the seventh end, deuces in the third, fourth, fifth, and a single in the first.
In the other games, Switzerland's Silvana Tirinzoni (1-0) downed Kristy McDonald of Winnipeg 9-5, and Sherry Middaugh (1-0) of Coldwater, Ont., scored a tie-breaking point in the eighth end of her 6-5 win over Edmonton's Val Sweeting.