"We all know how that story ends," the defending champion said as he changed sleds for the trek across the icy, often windy coast to Nome. "If history repeats itself, things are looking good."
King arrived at Unalakleet at about 2 p.m. Sunday, still running with all 16 dogs. Mackey followed 90 minutes later. But he was first out of the community of 750, leaving at 6:17 p.m., 44 minutes ahead of King.
Not that the 51-year-old from Denali Park is too concerned.
"I think I have more speed than he does," King said. "But clearly, this could be a race. I thought his team looked pretty good coming here."
Before taking off, King asked checkpoint volunteers for Mackey's departure time. But asked if that affected his own departure, he said: "No, it's about the time I was going to go."
Mackey led until King shot past him early Sunday after leaving the Kaltag checkpoint for Unalakleet, 261 miles from the finish line in Nome.
In Unalakleet, while King napped, Mackey fed his dogs and joked with locals, stopping to sign autographs on several parkas. He told veterinarians that he would drop two dogs that weren't performing as well, leaving him with 12.
Many of these dogs were with Mackey last year when he became the first musher to record back-to-back wins in the Yukon Quest International Sled Dog Race and the Iditarod. Mackey also won the Yukon Quest last month with many of the same dogs running in this Iditarod.
But the team has not been running to par with past races, while King's dogs have looked alert and strong.
Mackey's dogs have been hampered by diarrhea and dulled by unseasonably warm temperatures, which were starting to drop on Sunday. They have turned up their noses at food at some checkpoints.
Most were relishing their food at Unalakleet, and Mackey said they were taking a turn for the better, responding to medicine and cooler temperatures. They also stopped to rest for at least six hours after leaving Kaltag.
"Now's the time to start paying attention to the neighbors," Mackey said, referring to close contenders like King and veteran Paul Gebhardt, last year's runner-up, who was running third Sunday.
Almost two dozen mushers were heading to Unalakleet Sunday night. Among them were Sebastian Schnuelle of Whitehorse, Yukon; Kjetil Backen of Porsbrunn, Norway; three-time Yukon Quest winner Hans Gatt of Whitehorse; four-time Iditarod champion Martin Buser of Big Lake; and Two Rivers veteran Rick Swenson, the Iditarod's only five-time winner.
Eight mushers have scratched since the start of the race and one has been withdrawn. One dog has died.
On Sunday, rookie Rodney Whaley of Franklin, Tenn., scratched in Cripple with 13 dogs.
A field of 86 mushers remains on the trail.
The front-runners take about 10 days to make the trek, so the winner could cross the finish line under Nome's burled arch by Tuesday.
On the Net: www.iditarod.com