Her victory in Saturday's slalom at Semmering in Austria was the 23-year-old American's 15th World Cup win of 2018 and 36th overall in slalom, beating the record of the Austrian great Marlies Schild.
It did not come easy. Under pressure from her arch rival Petra Vlhova, Shiffrin held off the charging Slovak by 0.29 seconds after two runs on the Zauberberg, with Swiss Wendy Holdener in third place.
A disappointing fifth place in giant slalom the day before, in a race won by Vlhova, had left seeds of doubt. But Shiffrin reasserted her dominance in slalom to claim her 51st World Cup win in all disciplines.
It also broke her out of a tie for 14 wins in a year, a record she shared with Austrian Marcel Hirscher, who has also proved dominant in 2018.
Neither will race again until the New Year's Day event in Oslo, where Shiffrin will look to win the parallel slalom event under the lights in the Norwegian capital for the second time in a row and begin 2019 in identical fashion.
For someone who professes to care little for records, Shiffrin's tally is remarkable but not her main driving force.
"It's a little bit distracting," Shiffrin told reporters after her latest triumph. "Because I'm not chasing these records and sometimes it gets in my head like I should be thinking about the records and the thing that helps me ski fast is focusing on my skiing."
Schild, who claimed her victories in a 10-year span from 2004 until her retirement in 2014, was an inspiration for Shiffrin in her formative years.
"She was the best slalom skier of this generation and I wouldn't be here if I didn't have her to inspire me," she said.
"I hope my record doesn't stand forever. Because that means that I inspired some girl as much as Marlies inspired me and then the sport is coming to a new level," she added.
Shiffrin has won 13 of the last 14 World Cup slaloms, including two parallels, and all five run this season, including one parallel.
Only the great Ingemar Stenmark stands ahead of her for overall World Cup wins in the discipline, the Swede totaling 40 in his career.
Vlhova has emerged as her main rival and came close to an upset as she made inroads into the near half a second lead Shiffrin had compiled in a dominant first run.
"I think the big thing was I had a really good first run. So I had a little bit of time to play with," Shiffrin said.
Shiffrin has a near-500 point lead over Vlhova in the overall World Cup standings, having also secured two wins in super-G and a giant slalom victory to show her burgeoning versatility as more records are set to fall in the future.
Dominik Paris was another skier to finish 2018 on a winning high, underlining his dominance on the Stelvio course at Bormio to win the super-G, the final men's World Cup race of the year.
It completed a stunning double on home snow for the Italian, who took the downhill on Friday and has now compiled a record four World Cup wins at the venue.
Paris edged out Olympic super-G champion Matthias Mayer of Austria, with Norwegian Aleksander Aamodt Kilde in third place.