Swiss rider Ruegg wins opening UCI World Tour event in Australia
Ruegg (EF Education-Oatly) kept pace with the leaders heading into the final sprint in hot conditions to cross the finish line in third place behind Dygert but enough to claim the opening race of the UCI World Tour season.
She became only the second non-Australian winner in eight editions of the womens Tour Down Under.
Ruegg, 23, set up her overall victory with a powerful win in Saturday's second stage to hold a 15-second buffer over Dutch rider Silke Smulders (Liv Jayco AlUla) heading into the decisive 105.9km final stage in the Adelaide Hills.
The Swiss rider claimed the overall ochre leader's jersey by 13 seconds in 8hr 49min from Smulders with Norway's Mie Bjorndal Ottestad (Uno-X Mobility) third, 37 seconds behind the winner.
"It was quite a challenge today, they didn't make it easy for us, they tried a lot of moves, especially in the last two laps," Ruegg said.
"I was super nervous the whole day, I really wanted to bring it home, my team were amazing, I could save all my energy early and focus on the last two laps of the stage."
Dygert (Canyon-SRAM), who was part of the American gold medal-winning pursuit team at the Paris Olympics last year, swept to the front and held on to her advantage to win the final stage by one second from Smulders and Ruegg.
"We came here trying to get the GC (general classification) and a stage win, we worked really hard today to get that win," Dygert said.
Alyssa Polites (ARA Australian Cycling Team) took the Queen of the Mountain title from Poland's Dominika Wlodarczyk (UAE Team ADQ).
The six-stage men's Tour Down Under, in its 25th year, gets underway in Adelaide on Tuesday.