This is Toronto's first such streak of eight straight regulation defeats since 1985.
The Leafs have 80 points with just six games remaining and might have to run the table to give themselves a legitimate shot at a second straight playoff appearance.
They have two fewer games left than the Red Wings (82 points), the Columbus Blue Jackets (82 points) and the Washington Capitals (80 points) in the Eastern Conference.
Cody Franson and Joffrey Lupul scored for Toronto. Gustav Nyquist also had a goal for Detroit.
Jonathan Bernier, playing his third game back from a groin injury, stopped 24 of the 28 shots. Red Wings goaltender Jimmy Howard finished with 25 saves.
The Leafs got some help earlier in the day when the Capitals lost at home to the Atlantic Division-champion Boston Bruins. They got no such assistance when the Blue Jackets beat the Carolina Hurricanes in Raleigh, N.C.
Bad starts had been a concern for the Leafs for the better part of the past two weeks. It wasn't a problem Saturday against Detroit.
Right from the get-go, coach Randy Carlyle rolled through all four lines and got the results he desired. The Leafs outshot the Red Wings 8-4 in the game's first 10 minutes, then saw tangible evidence of having the puck in the offensive zone.
After Jay McClement won an offensive-zone faceoff against Helm, Jake Gardiner was right there to pass it to an open Franson. The defenseman, who was held without a shot in Friday night's loss in Philadelphia, sent one by Howard at 10:57 of the first.
In making that goal stand up the rest of the first period, the Leafs took a lead into intermission for the first time since March 10 at the Anaheim Ducks.
That didn't last long, thanks to struggles on the power play. A turnover by Phil Kessel at the blue line sprung Helm on a breakaway, and then, even after Bernier stopped him, a giveaway by Gardiner helped the Red Wings center score at 3:05 of the second.
Howard made a huge sliding pad save on Lupul less than a minute later to keep it a tie game.
At 4:37, Detroit's Nyquist scored to make it 2-1 with his 10th goal in the past eight games and 21st in the past 26.
The Leafs fell behind 3-1 at 7:57 of the second when Helm deflected Jakub Kindl's point shot past Bernier. The Red Wings' third goal of the night came on just their 14th shot.
A timely and crucial four-minute penalty kill followed, then Morgan Rielly and Lupul combined to give Toronto some life at 18:57. Rielly drove hard to the net and, as soon as he drew a tripping penalty, managed to swat the puck from along the ice to Lupul to cut the deficit to one.
Despite Lupul's 22nd of the season, the Leafs found themselves in a familiar spot: down a goal going into the third period.
The hole got too deep on Helm's third goal of the night 8:38 into the third period, when he took a pass from Danny DeKeyser, got past Franson and beat Bernier on the ensuing breakaway.
NOTES: The attendance was announced as 20,270, a season high at Air Canada Centre. ... Bernier started on back-to-back days for the first time this season and just the second time in his NHL career. The only previous time was March 5, 2013, with the Los Angeles Kings, when Bernier was pulled after giving up three goals on eight shots. ... Defenseman Paul Ranger and enforcer Colton Orr were scratched for the Leafs, who recalled forward Jerry D'Amigo earlier in the day from the AHL's Toronto Marlies. ... The Red Wings were playing their 14th straight game without star Pavel Datsyuk (knee) and 16th straight without captain Henrik Zetterberg (back). They've played 35 total without Datsyuk and 29 without Zetterberg. ... The game was broadcast live on CCTV in China.