The first goal in the snow-capped match came from Devon Sandoval, who finished simply on a rebound from a Sebastian Velasquez shot from outside the box.
Stephenson's goal, the 3-2 winner, came after a neat link-up between striker Robbie Findley and midfielder Ned Grabavoy. Grabavoy cut the ball back inside from wide right, and Stephenson wasted no time taking a shot, which skipped across the snow-ridden grass and into the back of the net.
The match also saw the first minutes from Olmes Garcia, who came in at the half alongside Joao Plata for Devon Sandoval and David Viana. Both played about 20 minutes before Jason Kreis sent out a more first-choice lineup.
Starting lineup: Saunders, Balchan, Maund, Salcedo, Palmer; Alvarez, Grossman, Martinez, Velasquez; Sandoval, Viana
68th minute lineup change: Attinella; Beltran, Schuler, Watson-Siriboe, Mansally; Beckerman, Grabavoy, Stertzer, Stephenson; Findley, Saborio
Real Salt Lake will make it to the final of the Desert Diamond Cup should New York not defeat Seattle; otherwise, tie-breaking scenarios would take place — New York would need to win by three or more goals. Seattle has already booked their spot in the final, as they're sitting with six points before their match tonight.