runoff election

Translations
второй тур выборов
The mayoral race was so close that it resulted in a runoff election.
Мэрская гонка была настолько напряженной, что потребовался второй тур выборов.
Definitions
A runoff election is a second round of voting held to determine a winner when no candidate receives the required majority of votes in the initial election. It typically occurs between the top candidates from the first round to ensure that the elected individual has broader support.