Corey Crawford made 31 saves for his second win in a row and third in five starts.
William Nylander scored to extend his point streak to four games for the Maple Leafs (25-17-7), who are 1-3-2 in their past six games.
"Very frustrating. I think when you go through these types of things, such as [an 8-4 loss at the Florida Panthers on Jan. 12], such as this, it's just a sign of where you are, that you're not when you want to be," Toronto coach Sheldon Keefe said. "Reality checks come. I thought we were an immature team down in Florida, I thought we were an immature team here today. That's how we're approaching these things. We're not performing; we're not playing with any level of discipline or consistency. That's what happens."
Frederik Andersen allowed six goals on 34 shots.
"I think it's time to just look in the mirror right now for everyone here, myself included," Andersen said. "I think it's not a time to point fingers or anything like that. I think you've got to use this week to reflect and make sure we come with more intensity and more purpose when we play after the [All-Star] break."
Caggiula gave the Blackhawks a 1-0 lead 21 seconds into the game when he banked a shot off Andersen's skate.