Robertson gave Dallas a 1-0 lead at 3:42 of the first period. He received a cross-ice pass from Joe Pavelski, cut back across the crease and scored as Sorokin was moving the other way.
Lee tied it 1-1 at 13:39, tapping in a backdoor slap pass from Brock Nelson on a power play.
The Islanders entered the game 2-for-36 on the power play in their previous 13 games dating to Dec. 10.
"The unit we had, we thought we had good looks," Nelson said. "Obviously, we had a tough stretch here. We weren't getting opportunities to go in, so to come out and get that one to tie it up, it's a big one. You want to win the special teams every night. Power play wants to contribute with at least momentum, but you want to contribute on the score sheet for sure."