Howard's rink from Coldwater, Ont., defeated a team skipped by Brad Jacobs of Sault Ste. Marie, Ont., by a count of 6-2 in just six ends, while Stoughton led his foursome over a fellow Winnipeg outfit led by William Lyburn 7-2 in seven ends.
Leading 2-1, Howard scored three in the third to stretch his advantage to four points. Jacobs responded with one in the fifth, but Howard added a single in the sixth.
Stoughton, meanwhile, blew open a tight 2-1 game in the fifth end by scoring four. Lyburn got one back in the sixth, but Stoughton restored the five-point lead with one in the seventh.
The round-robin tournament is the second men's Grand Slam event on the World Curling Tour and has a purse of $100,000.
In other scores, Jim Cotter of Kelowna, B.C., sent the hometown fans happy with a 6-5 victory in extra ends over Calgary's Kevin Koe.
With Cotter up 3-2 after five ends, Koe grabbed a 4-3 lead in sixth. Cotter retook the lead with two of his own in the seventh, but Koe tied the score 5-5 in the eighth to force the extra end.
Elsewhere, John Morris, who is skipping Kevin Martin's Edmonton rink, easily handled Switzerland's Peter de Cruz 9-1 in six ends, while Brad Gushue of St. John's, N.L., scored a 7-4 victory over Toronto's John Epping.
Howard and Stoughton sit atop Pool A, while Cotter and Gushue lead Pool B. Martin's rink is alone in first in Pool C.