Hector was 18 hundredths of a second ahead of Paula Moltzan and 23 hundredths of a second ahead of Mikaela Shiffrin, both from the United States.
The Swede led after the first run, and when she started the second she had half a second to spare. That margin shrank along the way, but was enough in the end for victory.
The victory was her eighth in the World Cup and the first in just over a year.
The giant slalom specialist came to the Czech Republic with three podium finishes under her belt this season. She was third in Kronplatz on Tuesday when she led after the first run.
It feels so good, I'm so happy to win, it's incredible. The audience was incredible, Hector says in the victory interview on Viaplay.
I'm super happy that I managed to be first across the finish line.
When asked if it was important to get a victory in the last giant slalom competition before the Olympics, the reigning Olympic champion replied:
Of course, it's always good to get a victory, but you always have to work hard because there are so many good skaters.
Hector is third in the giant slalom cup, after Julia Scheib of Austria and Camille Rast of Switzerland - Scheib competed in the Czech Republic, Rast came fourth.
Hanna Aronsson Elfman finished 15th and Estelle Alphand finished 26th.
There are slalom competitions in Spindleruv Mlyn on Sunday.
