The 25-year-old alpine queen followed up her victory in Friday's super-combined events in Val d'Isère, France with a third-place finish in Sunday's Super G, and that was enough to see her leapfrog Riesch, who finished in 21st place.
Vonn, who has picked up 518 points to date this season, said: "It's not looking too bad. It doesn't really matter at this point; we still have a lot of races left, but I'm happy to have taken some points for the super-G standings."
But the double world champion, who was denied the chance to claim a hat-trick of wins on the Oreiller-Killy course by adverse wind conditions on Saturday, was disappointed not to have gotten the better of Swiss duo Franzi Aufdenblatten and Nadia Styge in the Super G.
"It was not my best race," she reflected. "I was a little bit disappointed with my run today. I thought I didn't execute very well in the top part of the course. I missed the timing on one gate and I feel like I lost the rhythm for the rest of the top. I wasn't as aggressive as I should have been, but I picked it up on the bottom. All in all I'm happy with the day.
"Maybe it was a mistake to take the longer skis because the terrain made it really tight. I did not ski well enough but every race is important for the overall standings. I did my best."
Vonn was 0.26 seconds off the pace as Aufdenblatten claimed a surprise maiden World Cup win in a time of 1 minute, 26.43 seconds.
The 28-year-old, who was 0.23 seconds faster than compatriot Styge, reflected: "It was the ultimate goal of my career. I really wanted to be the fastest one day. It's a perfect day. I couldn't dream of something better."
FIS World Cup Downhill Overall Standings
1. Lindsey Vonn USA 581 points
2. Maria Riesch Ger 531
3. Kathrin Zettel Aut 384
4. Anja Paerson Swe 298
5. Elisabeth Goergl Aut 298
For more information, check the FIS World Cup website.