Corey Crawford made 24 saves in the victory and stepped up during the Lightning's final minute attack. Saad backhanded the game-winning goal past Vasilevskiy, who was making his first career playoff start. He made 17 saves in relief of Bishop, who is speculated to have a a lower-body injury.
Alex Killorn scored Tampa Bay's lone goal in the second period, as the Lightning's four-game road winning streak came to an end. Tampa Bay had plenty of opportunities to tie the game in the final minute, but could not capitalize. Steven Stamkos had the best look, sending a one-timer wide of the goal with less than a minute to play.
The Lightning still has home-ice advantage in a series that has turned into a best of three. The Blackhawks are now just two wins away from their third Stanley Cup in the past six seasons. This is the first Stanley Cup Finals since 1968 in which each of the first four games have been decided by just one goal.
Jonathan Toews got the scoring started in the second period, finding the back of the net for the first time since game 7 of the Western Conference Finals. The score would hold until Killorn tied the game just five minutes later. Saad's game winner was his second in two games, eighth of the postseason, and all eight have either tied the game, given Chicago the lead, or extended a lead.
Vasilevskiy became the fourth-youngest goalie to start a Stanley Cup Finals game in NHL history, and youngest since Patrick Roy did so at 20 years old in 1986.
The series will return to Tampa Bay for game 5 on Saturday night.