Williams performed a series of his hits, joined by Russian soprano Aida Garifullina, prior to the hosts' opening 5-0 victory over Saudi Arabia.
Ronaldo dummied the opening kick, allowing a child to pass the ball to mascot Zabivaka.
Russian president Vladimir Putin then gave a speech at the Luzhniki Stadium.
"We are sincerely happy to host the World Cup in our country," he said.
"Football is truly loved here. Russia is an open, hospitable and friendly country."