The 26-year-old Indian, who won a silver in the 2016 Rio Olympics, notched up a 21-15 21-13 win over 13th seed Blichfeldt in a 41-minute match.
Sindhu will next face the winner of the match between Akane Yamaguchi of Japan and Korea”s Kim Gaeun.
On Wednesday, Sindhu had defeated world No. 34 Hong Kong”s NY Cheung 21-9 21-16 to top Group J.
Sindhu is the lone Indian badminton hope left in fray after B Sai Praneeth”s maiden Olympic campaign ended in agony in the men”s competition.
He went down in straight games to Mark Caljouw of Netherlands for his second defeat in Group D.
On Tuesday, the men”s doubles team of Chirag Shetty and Satwiksairaj Rankireddy suffered a heartbreak after failing to make the quarterfinals despite winning two matches in their group.