Opponents of the anticorruption crusader Bernardo Arévalo delayed his inauguration as president of Guatemala on Sunday, ratcheting political tensions higher in Central America’s most populous country.

Confusion around the transition of power emerged shortly after Guatemala’s highest court on Sunday allowed conservative members of Congress opposed to Mr. Arévalo to maintain their leadership of the chamber.

After that ruling, arguments among lawmakers flared in the chamber around midday when Congress was expected to officially name Mr. Arévalo as president. Some congressional members went behind closed doors; as they remained deliberating, other lawmakers contended they were trying to derail the transfer of power, fueling bewilderment and frustration around the country.

“These are the latest strategies that corrupt elites are using to prevent a democratically elected government from coming to power,” said José Ochoa, 64, a small-business owner who was among the hundreds who streamed into the streets of Guatemala City’s old center to show support for Mr. Arévalo on Sunday.