McEwen scored four points in the second end and two more in the sixth en route to his third win of the day.
Earlier, McEwen took a lopsided 10-3 win in five ends over Japan's Yusuke Morozumi. The Winnipeg skip opened the day with a 7-1 thrashing of Edmonton's Brendan Bottcher.
Olympic champion Brad Jacobs is 1-2 after losing his last two matches of the day.
Jacobs' rink from Sault Ste. Marie, Ont., fell to Newfoundland's Brad Gushue 6-4 in Draw 5, and lost 8-4 to Niklas Edin of Sweden in Draw 4. Gushue scored two each in the fourth and sixth ends to pull ahead of the Sochi gold medallists, while Edin scored threes in the fifth and seventh ends.
Jacobs beat Regina's Brock Virtue in Draw 2 for his only victory of the day. Gushue is 2-0 with his first win coming against Edin in Draw 1 Thursday.
Defending champion Jeff Stoughton of Winnipeg is also 2-1 after a couple of short matches.
Stoughton scored three points in the first end and four in the third en route to an 8-1 win over Morozumi. Stoughton edged Edmonton's Brendan Bottcher 6-3 in six ends in the day's early draw.
Coldwater, Ont., native Glen Howard kept pace with Stoughton at 2-1 after a 10-9 loss to Switzerland's Sven Michel in the evening draw. Howard took a 7-4, seven-end win over Switzerland's Pascal Hess in Draw 3 and beat Toronto's Travis Fanset 6-3 in Draw 1.
Brier champion Kevin Koe improved to 2-1 with a 5-3 win over Fanset in Draw 4.
Koe's Calgary rink scored two in the fourth end and added single points in the fifth and seventh ends to seal his second victory of the day. Koe downed Mark Dacey of Halifax 11-4 in Draw 3 earlier.
Martin is 2-1 after beating Saskatoon's Steve Laycock 6-5 and Morozumi 6-5.
Michel is 3-0 after edging Howard, Fanset and Koe.
The tournament is the third instalment of the Grand Slam of Curling with the series finale Players' Championship scheduled for next month in Summerside, P.E.I.