Six-time winner Tiger Woods is one of five players who carded a 6-under 66 on Thursday and sit tied for the top spot after the first round of the WGC-Cadillac Championship at the TPC Blue Monster at Doral. World-number one Rory McIlroy, coming off his second-round withdrawal at the Honda Classic last week, continued to struggle with an up-and-down 1-over 73.