Chandler Stephenson had three assists, and Thompson made 37 saves for the Golden Knights (42-31-8), who have lost five of six (1-2-3).
"That's why you play," Stephenson said, referring to the playoffs. "From the beginning of the year, [training] camp, you're getting ready for the playoffs. It's obviously disappointing. It's not where we want to be but again, injuries and crazy injuries, too, throughout the year. Yeah, it's tough, for sure."
Raddysh put the Blackhawks ahead 1-0 at 16:01 of the first period when he skated in from the right wing, went behind the net and banked the puck in off the right skate of Thompson.
Michael Amadio tied it 1-1 at 17:39, taking a cross-ice pass from Shea Theodore and scoring on a one-timer from the goal line on the left side.
Raddysh scored his second at 19:59, poking in the third rebound of his own shot after Lafferty moved in and had his shot blocked. Linemate Philipp Kurashev also had an assist.
"We're hard on the puck," Raddysh said. "I feel like [Lafferty], [Kurashev] and myself just kind of forced their 'D' to turn the pucks over and got our chances off of that. On both of my goals, 'Laff' and 'Kursh' had some big turnovers and just led to opportunities for us, and I just happened to find the back of the net."