Jordan Spieth had his sister, Ellie, cheering him on Thursday at Whistling Straits

HAVEN, Wis. -- Jordan Spieth's biggest fan was in attendance on Thursday.

Huge galleries were walking with the marquee group of the afternoon at Whistling Straits. Thousands of golf fans hoping to get a glimpse of World No. 1 Rory McIlroy, British Open champion Zach Johnson and two-time major winner Jordan Spieth. One of those fans cheering on Spieth was someone who knows Spieth better than anybody: His little sister, Ellie.