After taking a cross-ice pass from Viktor Stalberg, Leddy fired from the left circle and beat Detroit's Jimmy Howard with a shot that slipped just under his glove. Leddy, a defenceman, said it was his first overtime goal at any level.
"It's an unbelievable feeling, one I'll never forget," he said. "I heard that stat (best start) before the game. If we stick to doing the little things, we'll be great."
The Blackhawks started 5-0 in 1971-72 — Hall of Famer Bobby Hull's final season in Chicago — and matched it on Saturday night with a 3-2 win in Columbus.
On Sunday, however, they were anything but assertive for much of the second and third period. Part of that was penalty-related.
Still, Chicago killed all six of Detroit's power plays, improving to 22 of 23 this season.
"We could have been on our heels a little bit," Chicago coach Joel Quenneville said. "Detroit was pressing (being) down a goal. You know everything's coming. They were pinching.
"We could have been better, but at the same time, six (games) in nine (days) could have been a factor."
Quenneville couldn't really fault his club, one of two undefeated NHL teams along with San Jose.
"I think everybody deserves credit," Quenneville said. "Everybody's contributing. Everybody was where we wanted them to be. Everybody had good conditioning to start with. Special teams, Crow (Crawford) in net, the team game. I'm pleased."
Crawford, who made his fifth start in six games, was sharp again. Last season, the Blackhawks' 28-year-old No. 1 goalie was criticized for allowing soft and untimely goals. That hasn't happened so far this season.
"Focus has been a huge part of it so far," Crawford said. "I thought I was focused last year, but I wasn't quite there.
"This year, I've paid a little bit more attention to that, especially throughout the game. Every play around the net, I'm ready and getting low for little things around the net so I don't give up those little goals."
Crawford needed to be sharp when his teammates sagged on Sunday.
"I thought we really carried the play in the last 30 minutes of the game," Red Wings coach Mike Babcock said. "They were better than us early. They outskated us, and then we really dug in and got playing a while. We had every opportunity to win the game."
Injury-depleted Detroit has gone just 2 for 26 with the man advantage so far.
"We've got to shoot the puck a little more and maybe things will be a little different," Franzen said. "It think it's just a matter of getting the shots and getting the traffic."
Howard, who has started all five of Detroit's games, made 25 saves.
Chicago has won four straight against Detroit, dating to Feb. 21, 2012. The Blackhawks and Red Wings met for the 722th time, the most of any two NHL opponents.
Sunday's game was only the Blackhawks' second at home, and they begin a six-game road trip Wednesday in Minnesota. The Blackhawks don't skate at home again until Feb. 12 as they play 10 of their first 12 games away from the United Center.
Keith scored the only goal of the first period, during a power play 2:24 in.
Crawford had to be sharp to preserve the lead in second. Early in the period, he made close-in saves on Todd Bertuzzi and Henrik Zetterberg. And the Blackhawks needed Crawford as they ran into penalty trouble in the second. Detroit was unable to convert any of four straight power plays beginning midway through the second, including a 43-second 5-on-3 advantage.
"The D were blocking the shots," Quenneville said. "Key saves by Crow (Crawford). It was a group effort, with spectacular kills.
"We dodged a bullet. It was the key to the game."
The Blackhawks started the third sluggishly, and Franzen finally tied it at 1 with an even-strength goal at 4:30 of the period. After Zetterberg's shot was blocked, Franzen picked up the loose puck and closed in from the right circle. He got by Keith and beat Crawford with a shot between the legs.
Crawford made a point-blank stop on Cory Emmerton midway through the third to preserve the tie.
Crawford stopped Franzen's prime chance 1:30 into overtime.
Notes: Red Wings D Jonathan Ericsson returned after missing three games with an injured hip. ... Detroit C Darren Helm (back) and D Jakub Kindl (healthy scratch) sat out after playing on Friday against Minnesota. Both have missed four of five games so far. ... Red Wings D Ian White (leg), D Carlo Colaiacovo (shoulder) and LW Jan Mursak (shoulder) and G Jonas Gustavsson (groin) remain sidelined. ... Out for Chicago were LW Daniel Carcillo (knee) and D Steve Montador (concussion, from last season) ... The 1971-72 Blackhawks won nine of its first 11 games en route to a 46-17-15 record and first place in the NHL's old Western Division.