Mrs. Kirchner wrote in a post on her website on Sunday that “Dec. 10 is not his birthday party.” She also noted one of her objections to holding the two ceremonies separately: she was in a hurry to leave the capital and get to Patagonia to see her sister-in-law, Alicia Kirchner, sworn in as a state governor there.

Mr. Macri then moved to curb Mrs. Kirchner. He obtained an injunction from a judge, ruling that her term ended at midnight Wednesday, rather than at midday on Thursday, meaning that she would have no official authority over the ceremony. Mrs. Kirchner responded by refusing to attend the swearing-in; to show solidarity with her, a number of lawmakers did the same. On Thursday afternoon, Mrs. Kirchner took a commercial flight to the Patagonian city of Río Gallegos with her son, Máximo Kirchner, a lawmaker, and her dog. Saying that she had actually been facilitating the transition, Mrs. Kirchner wrote that she had ordered the flower beds at the presidential residence to be reseeded for the new tenant.

In the end, Federico Pinedo, a lawmaker in Mr. Macri’s party, served as acting president between midnight and noon on Thursday, and it was he who placed the sash over Mr. Macri and handed him the baton at the presidential palace, as regional leaders looked on. From a balcony of the palace, Mr. Macri then spoke, and briefly danced, before crowds gathered in the plaza outside.

Mrs. Kirchner delivered a farewell speech to her supporters in the same plaza on Wednesday night. Positioning herself as an unyielding opposition leader, she accused Mr. Macri of using disagreements over the ceremony to distract attention from his plans for major changes in economic policy. Though she was barred by the Constitution from running this year for a third consecutive term, she is free to run again in 2019.