The American pipped Swiss star Lara Gut to victory by just 0.15 seconds and finished 0.48 seconds ahead of home favorite Viktoria Rebensburg in third.
"It feels amazing. I just got to the bottom, and I cried," a teary-eyed Vonn told FIS Ski after her second run at Garmisch-Partenkirchen, Germany.
"I worked really hard to come back and you know, I feel like sometimes I come back so quickly, everyone forgets how much time and energy, blood, sweat and tears it takes to come back without any training and just jump in there.
"And I had to trust myself and my team and my technician, and we all did our best and today was just amazing."
After finishing 13th in her first race since returning from injury in Austria
last week, Vonn's preparation in practice Friday was far from ideal.
The 32-year-old missed a vital gate in training, though she remained confident ahead of Saturday's run.
"I didn't really try very hard to make the gate yesterday," she explained.
"So I knew as long as I stood on it and I gave myself a little bit of extra room just so that I carried the speed through that section. It wasn't really in my head too much."
Vonn is now just nine World Cup wins behind Swedish legend Ingemar Stenmark's all-time record of 86.
She revealed last week that her broken arm -- suffered during training in Colorado 10 weeks ago -- was so severe, nerve damage meant she couldn't even more her right hand.
In the overall World Cup standings, Gut's second place finish sees her gain 80 points on leader Mikaela Shiffrin but still remains 235 points behind.
"I'm pretty happy because I know I can be close to the win all the time if I ski the way I can," a confident Gut said after the run.
There was some bad news, however, for World Cup newcomer Kajsa Vickhoff Lie. The Norwegian suffered a nasty crash at the bottom of the course and had to be evacuated from the slopes.
Gut wins super-G
Sunday's action at Garmisch saw a reversal of fortunes with Gut claiming victory in the super-G, with Vonn back in ninth after her heroics of the previous day.
Gut has won all three races in the discipline this season as she relegated Stefanie Venier of Austria to second place with Tina Weirather of Liechstenstein completing the podium.
Her victory has seen her close to within 135 points of slalom specialist Mikaela Shiffrin in the race to win the overall title, which Gut is defending.
Vonn finished her run 1.65 seconds adrift and admitted "I still have a lot of work to do."
"It was icy and I chose the wrong skis.
"In my head I was ready, but while the confidence is there in the downhill, something is missing in the super-G," she added.
Vonn is targeting the world championships to be held in St. Moritz, Switzerland, from February 6-19 to hit top form.
Hirscher wins as Briton makes mark
In men's World up action Sunday, Austria's Marcel Hirscher took a giant stride towards a sixth straight overall title with a stunning victory in the slalom at Kitzbuehel.
The 27-year-old produced a stunning second leg to win by 0.76 from Dave Ryding, who led after the first runs.
Ryding was making history of his own, equaling the best result in World Cup competition by a British skier, the second place of Konrad Bartelski's in the 1981 Val Gardena downhill.
Russian Alexander Khoroshilov came in third for his eighth podium finish, 1.11sec off the pace.