LONDON: British pop star Robbie Williams fought a bad case of flu to perform for 20,000 fans in South Africa. Williams was advised not to go ahead with the two-hour show but he was determined not to let his fans down, contactmusic.com reported. Though he went ahead with the performance, Williams felt his energy levels dip midway through the show. He joked: “I do not know how Mick Jagger does this. I am 32 and I am knackered. He is like 110, or something.”