Shiffrin came into Friday's race, her first since winning the gold medal in giant slalom and silver in alpine combined at the 2018 Olympic Winter Games, with a 561-point lead over Switzerland's Wendy Holdener, who finished 14th Friday.
Shiffrin won slalom gold at the 2014 Sochi Olympics at the age of 18, a year after she won the first of her three consecutive world slalom titles.
Two-time Olympic champion Mikaela Shiffrin can clinch her second overall world cup title with strong performances this week in Ofterschwang, Germany.
Shiffrin follows Lindsey Vonn as only the second American woman to win multiple World Cup titles, while she can add the slalom globe on Saturday.
She was a clear favorite to successfully defend her maiden overall title since setting a World Cup record by winning the first five races of 2018.
Shiffrin also leads the slalom standings with two races left and can wrap that up on Saturday with a 10th place or better in Ofterschwang.
Shiffrin has enjoyed a dominant season, topping the World Cup podium 11 times.
"After past year when I won the overall, actually some people were saying like it's sort of fake because the other girls weren't there and there was nobody to challenge her". She skipped the downhill but picked up silver in the combined. "I knew my skiing was solid".
The American duly wins for the second successive season with five races still remaining. "But nothing is impossible, so I am going to stay focused". Rebensburg leads the overall giant slalom standings by 92 points over Tessa Worley of France.