"He was in there right with us too," Toronto coach Mike Babcock said. "Coach, players, goalies, everybody, we were bad, so let's get on the flight and let's get regrouped.
Tyler Bozak scored on the power play at 13:50 to make it 3-1, but Ritchie pushed the Dallas lead to 4-1 at 16:04 when he went to the net and finished a pass from Julius Honka.
Jamie Benn gave the Stars a 5-1 lead when he beat McElhinney with a wrist shot on the power play with 1:38 left in the first.
"I don't know what it is, we were just kind of flat-footed, and they came out hard," Bozak said. "They're a good team, and you got to give them credit. They made the most of their chances early in the game and kind of put us behind."
Toronto capitalized on a turnover by Honka, and Nikita Soshnikov scored his third goal of the season to make it 5-2 at 4:19 of the second period.
Jason Spezza gave Dallas a 6-2 lead at 7:49 of the second when he scored on the rebound of Seguin's wraparound attempt.
Mitchell Marner scored at 10:25 of the second to make it 6-3.
Toronto appeared to score with 8:43 remaining in the third period to get within two, but the goal was disallowed after video review showed Soshnikov kicked Lehtonen's stick to put the puck in the net.
"I wasn't worried the first couple minutes because I thought their guy just pushed me into the net before the puck," Lehtonen said. "But the replays revealed some more stuff. Yeah, it was good because there would have been lots of time left."