Worley, the first leg's pace setter, produced a pair of superb runs on a deteriorating course to finish 0.34 seconds ahead of American Mikaela Shiffrin, with Italy's Sofia Goggia taking the bronze medal.
With warm weather making the course tougher for the top contenders in the second leg, Worley recovered from a slight glitch which threw her off balance in the top section.
"The pressure was pretty high before the second run but I managed to go to the end and win it," a delighted Worley told the race organisers.
"I knew just a small mistake like this could be fatal and I just told myself to push harder and it was enough."
It was a triumphant return to the pinnacle for 2013 giant slalom world champion Worley, who missed the 2014 Olympics with a serious knee injury which also cut short her World Cup season the same year.
Overall World Cup leader Shiffrin, the hot favourite in Sunday's slalom, was third after the first leg but leapfrogged Goggia into the silver medal position with a strong second run.
Goggia, who edged compatriot Federica Brignone to the bronze medal, produced Italy's first podium finish in the championship which continues with the men's giant slalom on Friday.
Defending champion Ana Veith finished a disappointing 22nd and Michaela Kirchgasser, who won the bronze medal in the combined event, came in 12th on a tough day for the Austrians.
Their less fancied compatriot Stephanie Brunner was the nation's top performer of the day with a fifth-placed finish as Bernadette Schild finished 17th after a huge second-leg error.
(Writing by Zoran Milosavljevic; Editing by Jon Boyle)
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