The Islanders struck first when Michael Grabner raced in and wired a wrist shot into the top corner on Joey MacDonald just three minutes into the game.
However, Calgary took over the game in the second period scoring four straight goals to jump in front 4-1.
TJ Galiardi, Lance Bouma and Curtis Glencross into an empty net also scored for Calgary, which also beat the Islanders 4-2 in another split squad game in Regina. The Flames played their fourth and fifth games of the pre-season and improved to 3-2.
Griffin Reinhart, New York's fourth overall pick in 2012, and Riley Wetmore also scored for the Islanders, who were playing their first two pre-season games.
Tied 1-1, Wideman scored his first of two goals at 7:39 on a long shot from the blue-line that deflected off an Islander and past goaltender Kevin Poulin.
The goal came shortly after Wideman threw a text book hip check along the side boards that sent Cal Clutterbuck upside down and drew a loud cheer out of those in attendance at the half-filled Scotiabank Saddledome.
Wideman added his second goal later in the second on a five-on-three power play. Showing tremendous patience, Wideman moved into the low slot and waited for an opening before zipping a shot past Anders Nilsson, who replaced Poulin halfway through the period.
Galiardi, a Calgary native who also played for the Western Hockey League's Hitmen, added another power-play goal 48 seconds later and it was a beauty as he neatly stepped around Nilsson in close and zipped a shot under the crossbar. Galiardi was acquired by the Flames from San Jose in July in exchange for a fourth-round draft pick.
Galiardi was the best player on the ice all night. He also made a strong play along the boards to set up Wideman's first goal. In one rush, he made a pretty toe drag move and nearly snapped in a goal.
He has been converted to centre by Flames coach Bob Hartley as Calgary is lacking depth at that position and, so far, it's been a success.
Notes: Galiardi went 11-11 in 22 faceoffs ... Clutterbuck left the game early in the third period favouring his leg. He was shaken up after delivering a heavy hit on Paul Byron ... MacDonald went the distance in net for Calgary, finishing with 18 saves ... Poulin finished with 14 saves on 16 shots while Nilsson turned aside 11 of the 13 shots he faced.