Atherton, 28, whose winning run goes back to June 2015, finished 0.7 seconds ahead of compatriot Tahnee Seagrave in Lenzerheide in Switzerland.
France's Myriam Nicole was third and Britain's Manon Carpenter fourth.
Hart, 24, beat American Aaron Gwin by less than 0.01secs to earn his first World Cup win.
South Africa's Greg Minaar was third.
Atherton's win was the 31st of her World Cup career. She has won the five World Cup races this year to add to six successive victories to end last season.
Rachel Atherton claimed an 11th UCI Mountain Bike Downhill World Cup win in a row as fellow Briton Danny Hart secured victory in the men's event.