The Swedish tennis jump started the tournament by defeating the Frenchman Benjamin Bonzi with 2-0 in sets (7-5, 7-5).
He followed that up with an even more convincing victory in the next match, against eighth-seeded South Korean Kwon Soon-Wo, 6-2, 6-3 in sets.
Thus, the 23-year-old is ready for the quarterfinals and is approaching his best record on the ATP tour.
In Winston-Salem, Mikael Ymer reached the first final of his career last year, but was defeated by Ilya Ivasjka from Belarus.
Next up is the winner of the meeting between Frances Tiafoe, USA, and Australian Thanasi Kokkinakis.
The tournament in Adelaide is part of Ymer's final preparations for the first highlight of the season: the grand slam tournament Australian Open in Melbourne starting on 17 January.
Last year he went to the third round, his best result there so far.
As 94th in the world rankings, Mikael Ymer has already qualified for the Australian Open.
However, it is not the older brother Elias Ymer, who from his 170th place in the ranking must qualify.
The qualifying tournament starts on Monday.