The Trump administration on Tuesday amended its Russia sanctions program, paving the way for aluminum giant United Co. Rusal to escape from the blacklist and granting the metals market a reprieve from a supply scare that rocked markets over the past month.

Facing delisting from the London Stock Exchange this week, Rusal’s owner, EN+ Group, sought the 11th-hour amnesty from the U.S. Treasury late last week by pledging that its majority shareholder and a primary target of the U.S. sanctions, Russian tycoon Oleg Deripaska, would...