Zirkle, who had reached Nikolai at 9:14 a.m., leads the pack of 66 mushers competing in the 40th annual sled-dog race from Willow, near Anchorage, to Nome. Defending champion John Baker was in second place, 22 minutes back. Rounding out the Top 5 were four-time winner Lance Mackey (9:59 a.m.), Hugh Neff (10:05 a.m.) and Ray Redington Jr. (10:22 a.m.).
The Anchorage Daily News reported the race's oldest musher, 74-year-old Dan Seavey, reached the Rainy Pass checkpoint at 10:19 a.m. on the race's third day.
Zirkle, who was running about an hour behind Baker's record-setting pace of last year, overtook Neff shortly after leaving Rohn and completed the 75-mile leg to Nikolai in 13 hours, 48 minutes. She had covered about 275 miles total.
"She is moving along steadily and is doing what she wanted to be able to do at this point in the race," a post on her kennel's Facebook page said. "Many of the dogs on her team have already run a thousand mile race. This is allowing her to keep a strong pace and doesn't seem to be lacking speed."
Notable deaths of 2014 [PHOTOS]