Hoefl-Riesch won for the first time in 11 months to kickstart her defence of the World Cup overall title she took from Vonn last season.
Vonn was last to race in the slalom leg, after being fastest in the morning super-G run, and threw back her head in frustration on seeing how close she was to winning for a third straight day. She smiled as her German friend approached in the finish area and hugged her in congratulation.
"It would have been nice to have a hat trick," Vonn acknowledged. "I'm really happy for Maria — but I'd rather she beat me by a second."
Still, Vonn earned 80 points and extended her lead to 387 over Tina Maze of Slovenia, who placed fifth Sunday.
Marie-Michele Gagnon of Lac-Etchemin, Que., was the top Canadian in seventh. It was her second top-10 result of the season.
“It was good to be 30th after the super-G so I had a clean course for the slalom," Gagnon said. "The slalom was a pretty hard set – it was tricky and quite tight.”
Hoefl-Riesch, who is third overall, trailed Vonn by 0.23 after the super-G but just edged the American on a flat slalom course slowed by warm sunshine.
The German racer had a combined two-run time of two minutes 8.41 seconds. Nicole Hosp of Austria was third, 0.51 back, after finishing 28th fastest in super-G.
"I'm really happy to be winning again. It's obviously the best," said Hoefl-Riesch, who had been runner-up three times this season, including behind Vonn in Saturday's downhill.
"In the speed events it's so hard to beat Lindsey so I was hoping to take the chance at the right time. Today, it was the right time," she said.
Hoefl-Riesch's 21st career World Cup win was her first since a super-G at Are, Sweden last February. As defending World Cup champion, she has struggled for consistent results after missing some off-season training.
Her first maximum 100-point tally came after Vonn has posted eight victories this season, and Hoefl-Riesch trails her great rival by a daunting margin of 554.
Marie-Pier Prefontaine of Saint-Sauveur, Que., finished 38th.
Vonn said she "never doubted" that her biggest rival during her three-year reign as overall champion would return to form.
"It always takes a while when you have setbacks," Vonn said. "It wasn't really a surprise for me that she has won."
Vonn was aiming to reach 50 career World Cup victories after also winning another super-combined event here on Friday.
She leads the super-combined standings after two of the scheduled three races, and can clinch the crystal globe trophy for a third straight year on Feb. 19 at Sochi, Russia. Sunday's race was a makeup for one cancelled last month at Val d'Isere, France.
Vonn will be strongly favoured to reach her landmark 50th win next weekend when her specialist speed events, downhill and super-G, are scheduled at Garmisch-Partenkirchen — Hoefl-Riesch's home town.
"Maria is going to give me a run for my money," Vonn predicted.
With files from The Canadian Press.