Koe's Calgary rink scored four in the first end and cruised to victory in Draw 6 action, needing just five ends to improve to 4-0 at the tournament.
Fowler, from Brandon, Man., managed just one point in the second end and fell to 1-2.
Edmonton's Kevin Martin (3-0) is the only other undefeated skip. He was idle for the first two draws Friday before facing Brad Gushue of St. John's, N.L., in Draw 8.
Glenn Howard of Coldwater, Ont., stayed with the leaders, scoring two points on his last rock in a 7-5 win over Norway's Tommy Ulsrud in Draw 7.
It was the second win of the day for Howard, who beat Rob Rumfeldt of Guelph, Ont., 5-2 in Draw 6.
Also in Draw 7, Winnipeg's Jeff Stoughton suffered his first loss, falling 7-5 to Switzerland's Peter de Cruz. Stoughton and de Cruz are both at 3-1.
Winnipeg's Mike McEwen evened his record at 2-2 with a 9-6 win over John Morris of Vernon, B.C. Morris fell to 1-3.
Toronto's Mark Kean moved to 3-1 with an 8-4 win over Rumfeldt (2-2).
And Toronto's John Epping joined the four-way logjam at 3-1 with a 7-4 win over Edmonton's Brendan Bottcher (1-4).