"I thought to myself it would be really important at these kind of things to not cause an international incident – and do you know what, I managed it," Robbie joked.
He then answered the question of whether he regretted the gesture with: "Yeah, of course. I can't trust me, I cannot trust me...I don't know what I'm going to do at any time."
"The plan was sing in key, don't fall over. That was the plan, and 99% of the plan I pulled off," he added.
Middle finger aside, Robbie's performance at Moscow's Luzhniki Stadium went without a hitch and was followed by a speech from Vladimir Putin, before the first ball of the 2018 World Cup was kicked.
Perhaps wisely, the singer decided to omit 'Party Like A Russian' from his setlist, sticking to hits including 'Let Me Entertain You' and 'Rock DJ'.
Ahead of the ceremony, many onlookers had criticised Robbie for accepting the gig.
Labour MP Stephen Doughty was one of them, stating (via the Guardian): "It is surprising and disappointing to hear that such a great British artist as Robbie Williams, who has been an ally of human rights campaigns and the LGBT+ community, has apparently agreed to be paid by Russia and Fifa to sing at the World Cup opener."