Crosby tied it 1-1 on a power play at 11:17. Guentzel deflected a slap shot from Kris Letang that became lodged under Shesterkin's left pad before Crosby jammed it over the line.
Mike Matheson and Guentzel scored 24 seconds apart to give Pittsburgh a 3-1 lead early in the second period. Matheson put the Penguins ahead 2-1 at 3:14 with a shot that deflected off Rangers forward Frank Vatrano's skate, and Guentzel tapped in a pass from Rust at 3:38.
Crosby had the secondary assist on Guentzel's goal for his 200th playoff point. He is the sixth player to reach the milestone, joining Wayne Gretzky (382), Mark Messier (295), Jari Kurri (233), Glenn Anderson (214) and Jaromir Jagr (201).
The Penguins captain has nine points (two goals, seven assists) in this series, tied for second with Boston Bruins forward Brad Marchand for the NHL lead.
"He's playing really well for us," Sullivan said of Crosby. "He's played some real good hockey in the playoffs in my time here, so that bar is really high. … He's playing an inspired game. He inspires the group just through his actions when he's on his game the way he is right now."
Mark Friedman extended the lead to 4-1 at 11:22 with a wrist shot glove side, but Adam Fox cut it to 4-2 at 14:04, spinning in the left face-off circle for a shot that went in off Matheson.
Danton Heinen made it 5-2 at 18:53 by deflecting a shot from Letang before Jeff Carter did the same on a shot from Jason Zucker, pushing it to 6-2 at 19:28.
The Penguins outshot the Rangers 16-11 in the second.
"We weren't playing very good in front of [Shesterkin]," New York forward Andrew Copp said. "It definitely wasn't on him at all. It's going to be up to every guy in the room to pull together and do what we can to win Game 5."
Evgeni Malkin scored on a backhand at 12:22 of the third period for the 7-2 final.
"Obviously, [Shesterkin] is a heck of a goalie," Carter said. "Arguably the best goalie in the League all year. So, we're trying to make it tough on him, get pucks and bodies there. Luckily, we've had some success here."