MOSCOW — Ruled by the same authoritarian leader since the 1991 collapse of the Soviet Union, Kazakhstan finally has a new president, with lopsided election results released on Monday confirming the victory of the old order’s handpicked candidate in a tightly controlled vote marred by hundreds of detentions.

Preliminary official results from Sunday’s vote showed that Kassym-Jomart Tokayev, the governing party’s chosen successor to President Nursultan Nazarbayev, had won 70.7 percent of the vote, far ahead of his nearest rival, an officially sanctioned opposition candidate, Amirzhan Kosanov, who received only 16 percent.

The election was denounced as unfair by observers from the Organization for Security and Cooperation in Europe. The organization, in a statement on Monday, said the poll had taken place “in a political environment dominated by the ruling party” and been compromised by “irregularities on Election Day and a disregard for formal procedures” that meant “an honest count could not be guaranteed.”

Mr. Nazarbayev, the country’s 78-year-old former Communist Party chief, announced in March that he was handing over his presidential powers to Mr. Tokayev, while retaining his posts as head of the security council and the governing party.