In his first game in an Islanders uniform, veteran goalie Evgeni Nabokov stopped 15 of 16 shots in two periods.
The 36-year-old refused to play for New York last season after the Islanders claimed him late in the year off NHL re-entry waivers, thwarting the Detroit Red Wings' attempt to sign him.
Nabokov was a 44-game winner with the San Jose Sharks in 2009-10 before struggling most of last season in the KHL.
This season, he has decided to join New York and he is competing for a roster spot with incumbent starter Rick DiPietro and rookie Al Montoya, who had an impressive 9-5-5 finish to the season after being recalled from the minors in mid-February.
The only offense Karlsson on Tuesday would need came at 4:10 of the second period on a nice short-handed goal by Glencross, who is coming off a career-high 24-goal season that earned him a $10.2-million, four-year contract.
Matt Stajan gained the Islanders blue line and cut to his left, threading a pretty pass to Glencross behind the Islanders' defense. Glencross continued across the top of the goal crease and tucked a backhand behind Nabokov.
Calgary added a second goal at 4:21 of the third period when Lee Stempniak finished a two-on-one with Alex Tanguay, taking a perfect set up from the Flames' veteran playmaker and scoring his second preseason goal behind Nabokov's replacement, Mikko Koskinen.
New York, which was playing just its third game, fell to 1-2-0 with two games remaining in a shorter than normal five-game preseason schedule.
Calgary improved to 2-3-0 with one preseason game remaining.
Notes: The Islanders sat several regulars including forwards John Tavares, Michael Grabner, Matt Moulson, and Kyle Okposo... Former Flames defenseman Steve Staios played in his third straight game for the New York. The 38-year-old is in the Islanders camp on a tryout basis... Jarome Iginla (back) is still not back skating. Rene Bourque is also nursing a nagging injury and isn't likely to return until the season opener. Veteran C Brendan Morrison (offseason knee surgery) is skating, but has not been cleared for contact.