Thirty minutes before the Group A opener between hosts Russia and Saudi Arabia, the show began with a performance of work by celebrated Russian composer Pyotr Tchaikovsky.
He was singing and dancing in front of the crowd of 80,000 at Luzhniki Stadium (and millions watching him live on television worldwide) when Williams suddenly stared directly into one of the ground cameras and flipped his finger!
While the opening fixture of Russian Federation v Saudi Arabia isn't exactly the high-profile affair of past World Cups - we were treated to Brazil v Croatia in 2014 - barely anyone could contain their excitement.
The game was screened by ITV in the United Kingdom, with host Mark Pougatch joined by Gary Neville, Slaven Bilic, Ian Wright and Lee Dixon - not that many watching actually noticed who the pundits were.
The opening ceremony of FIFA World Cup 2018 saw the cheekiest moments when British popstar did the unthinkable.
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"Football is truly loved here. I felt that in Brazil four years ago and I am now happy to share this excitement with the Russians as well". Together with the Original Trophy we have traveled all around Russian Federation - from Kaliningrad to Vladivostok - and everywhere we saw the highest level of readiness for the upcoming FIFA World Cup. England will have representation in the opening ceremony in the form their 90s pop icon.
Yes, perplexingly, one of Britain's most famous pop stars was opening the event but, shockingly, that isn't what got everyone talking.
The national anthems were then played, and sung gustily, handshakes were made and the 2018 World Cup's first game kicked off with a match ball that spent March orbiting the earth in the International Space Station.
Speaking to Reuters on Tuesday after a rehearsal for the show, Williams said he will be performing "a medley, a smorgasbord of my greatest hits" alongside Russian soprano Aida Garifullina. This year there will be a strong focus on musical acts.
Having faced criticism over lengthy opening ceremonies in the past, Federation Internationale de Football Association kept proceedings short on Thursday.