Toronto has allowed a league-worst 37 goals this season while Atlanta and Los Angeles are next on that list with 36 apiece.
Poor goaltending is only one part of the problem for the Maple Leafs (3-4-2) and Thrashers (1-7-0).
Toronto acquired Vesa Toskala from San Jose in the offseason to hopefully take control of the starting job.
Toskala, though, is 2-3-0 with an ugly 3.99 goals-against average, which ranks among the league's worst. Andrew Raycroft, the starter most of last season, has been slightly better, going 1-1-2 with a 3.64 GAA.
The Maple Leafs' porous defense was exposed again on Saturday as they squandered a two-goal lead in the third period and lost 6-4 to visiting Chicago. It was the fifth time this season that Toronto entered the third period either leading or tied and failed to come away with a win.
Captain Mats Sundin had two goals for the Leafs, who have been outscored 16-8 in the third period this season.
"We started good," center Alex Steen told the Maple Leafs' official Web site. "We had a couple big goals from Mats. It all comes down to the third period. We need to play a much, much better third period."
Poor special teams and undisciplined play have also contributed to Toronto's disappointing start. The Leafs are a dismal 5-for-45 on the power play and have been short-handed a league-high 61 times.
Making matters worse for the Leafs is the absence of rugged right wing Darcy Tucker, who is out indefinitely with ligament damage in his right knee.
"We don't know how extensive it is or how long it will take time-wise," Tucker said after receiving treatment Monday. "As of now, it's indefinite. Hopefully, I'll get a brace made and we'll see how it progresses from there."
Sundin has been a bright spot, ranking among the NHL leaders with 14 points. He has five goals and 21 assists in 24 career games against Atlanta, his last goal coming Jan. 30, 2003.
Two nights after recording their first win of the season, the Thrashers opened a seven-game road trip Saturday with a 6-2 loss to Tampa Bay.
Ilya Kovalchuk and Brett Sterling scored for the defending Southeast Division champion Thrashers, who have been outscored 21-4 in losing all four road games.
Johan Hedberg allowed five goals on 24 shots over the first two periods Saturday before he was replaced by Ondrej Pavelec, who stopped five of six shots in his NHL debut.
"We hung Moose (Hedberg) out to dry a little bit," Thrashers general manager and interim coach Don Waddell said.
Hedberg has allowed two goals in each of his last three starts versus the Maple Leafs, and is 5-4-0 with a 2.80 GAA in nine career appearances against them.
Atlanta is off to its worst start since going winless in its first 10 games of the 2002-03 season.
The Leafs had won eight straight against the Thrashers before going 0-2-1 in the final three meetings last season. Toronto is 6-2-1 with one tie in its last 10 home games against Atlanta.