Jason Day conquers course and illness to lead the field

There were no fist-pumps and high-fives from Jason Day after he stormed to the halfway lead in the opening leg of the FedEx Cup playoffs.

The only reaction the Australian could muster after shooting a second consecutive round of four-under-par 67 to forge a one-stroke advance over the field was a wry smile, a handshake and a wave to the crowd. The 22-year-old is no introvert, but is suffering from a mystery illness that has left the doctors baffled and left him drained of strength. He knows only too well that he needs to conserve every ounce of energy.

"Most of the guys that have been with me the whole year have known that I'll get really tired, real weak and shaky out on the course and I just really can't do much at all," he said.

Day said he had been suffering from the illness all year. Some doctors think he is suffering from the viral infection mononucleosis, others suspect he has Lyme disease.

"I've seen like eight doctors, can't get a straight answer," he said. "My agent wants me to see someone this Monday but it's very unlikely that I'm going to go and see someone. So I'm going to wait until after the FedEx and try and get this sorted.".