“I’ll have a balanced economic cabinet,” Mr. Macri said of his choices for top economic policy posts, declining to say who would fill them while drawing a contrast with previous governments on the left and the right in which star economists have wielded substantial power over other ministers.

Dressed in a blue shirt without a tie, Mr. Macri greeted other questions with the barest of smiles while sitting in a hotel lobby. At the end of a long campaign, he seemed neither exhausted nor dazed, resembling instead someone who might have emerged from a session of meditation.

Hewing to his plan to restore investor confidence in the economy, Mr. Macri calmly criticized what he views as the unreliability of official statistics in Argentina. He avoided mentioning Mrs. Kirchner or Mr. Scioli by name. Touching for a moment on a politically delicate subject, he said he planned to review a deal with China to build a nuclear reactor in Argentina.

Some political analysts question how a Macri presidency would deal with Peronism, the ideologically diverse political grouping that has long dominated Argentine politics. Still, other analysts say that Mr. Macri has made strides in reshaping Argentina’s political landscape, especially with the victory of a rising star in his party, María Eugenia Vidal, who was recently elected to the coveted governorship of Buenos Aires Province, a Peronist stronghold. Ms. Vidal’s triumph, they said, has lifted a veil of doubt about Mr. Macri’s ability to govern beyond the city of Buenos Aires, a pocket of relative prosperity enclosed by poorer sprawl not covered by his administration. Those surrounding areas are home to nearly a quarter of Argentina’s population. Crucially, mayoral races across the province were also won by Mr. Macri’s candidates, easing fears of struggles between Ms. Vidal and influential Peronist power brokers.

“The geography of Argentine politics has changed,” said Julio Burdman, an Argentine politics professor.

Some are even suggesting that the only issue at play on Sunday is Mr. Macri’s margin of victory. A poll by Elypsis, a political research firm that accurately predicted the first-round result, gave Mr. Macri 47 percent of the vote, against 39 percent for Mr. Scioli, with 11 percent undecided. The survey, taken on Nov. 16 and 17 in interviews with 2,200 people around the country, had a margin of sampling error of plus or minus three percentage points.

A small margin of victory may not be enough to give Mr. Macri a mandate, wrote Carlos Pagni, a political commentator, in the newspaper La Nación. “Macri needs a conclusive victory to carry out reforms that would allow him to relaunch the economy,” Mr. Pagni wrote.