Mackey, of Fairbanks, left three hours and 27 minutes ahead of Nenana's Aaron Burmeister after flashing 9 mph speed no other racer could approach on the 90-mile run from Ophir to Iditarod.

He didn't slow much on the 65-mile run to the small village of Shageluk, either, averaging 8.3 mph to arrive at 7:35 this morning. No other musher was in sight.

Kukokwim 300 champion Mitch Seavey was the second fastest over the long stretch into Iditarod, but he averaged nearly 3 mph slower than Mackey -- a huge difference in this sport.

"The trail conditions are a big surprise out here," said former Iditarod racer Bruce Lee, who is doing race commentary on the Iditarod's Web site. "At the mushers meeting before the race started and all trail reports since that time ... we all heard stories of 2½ feet of fresh snow on the ground in this general area.

"What we're seeing here is a fairly solid crust which holds the dogs. In fact it's so solid it supported the weight of our helicopter when we set down along the trail to check out conditions."

For years, front-running Iditarod mushers have sought to build a gap sizeable enough that they were leaving a checkpoint as the chasers were arriving, discouraging those trying to catch up..

Mackey is approaching that ideal, pulling out of Iditarod, just two hours, 28 minutes after Burmeister arrived. He also rested at the isolated checkpoint, where he earning $3,000 in halfway money, 28 minutes longer than Burmeister -- and more than two hours longer than some of his other pursuers.

Now the key may be the trail conditions ahead, and Mackey's speed into Shageluk suggests they did not deteriorate much.

As Mackey neared Iditarod on Thursday, he looked plenty comfortable, turning around on his sled as his dogs climbed a hill to scan the open terrain behind him.

If he was looking for pursuers, he found none.

As Mackey and his 16 dogs build their lead, forecasters say the weather will turn cooler, closer to what he's used to training in Fairbanks much of the winter.

Lower Yukon Valley temperatures are expected to dip to minus-10 on Saturday night, according to the National Weather Service. That's the coolest they've been so far in this Iditarod.

Once Burmeister was back on the trail at 3:10 a.m., other mushers began to stream out of Iditarod.

Yukon Quest champion Sebastian Schnuelle of Whitehorse in the Yukon, left five minutes later, and Seavey took to the trail 49 minutes behind Burmeister.

Behind them came Cim Smyth of Willow, out at 4:23 a.m.; Hugh Neff of Skagway, out at 4:25 a.m.; two-time runner-up Paul Gebhardt of Kasilof, also out at 4:25 a.m.; four-time champion Jeff King, out at 5 a.m.; and top Kotzebue racer John Baker, out at 5:23 a.m.