Oosthuizen, the 2010 Open champion, was 4 over through eight holes when he pulled out after teeing off on No. 9. The South African says "as the round progressed, the pain in my neck translated into my hips and I found it increasingly uncomfortable to walk."
Oosthuizen withdrew from last month's U.S. Open at Merion after the first round, citing a hip problem.
Hanson, a Swede who played for Europe at last year's Ryder Cup, lasted just five holes before pulling out with a back injury that had troubled him before the tournament. He was 2 over par.