Mackey rolled through the Rohn checkpoint near sunset and headed towards the Farewell Burn with 15 dogs still in harness. The Fairbanks musher often stops to rest not far out of Rohn.

His friend Hugh Neff of Tok -- who has battled Mackey in the Iditarod and, particularly, the Yukon Quest for years -- gave chase 29 minutes later.

But the early speed of the 39th Iditarod was startling.

Mackey made the 48-mile run from Rainy Pass to Rohn at a jaw-dropping average speed of 13.2 mph. While the run is largely downhill, it includes a notoriously nasty section through the Dalzell Gorge replete with sharp switchbacks. It has brought more than one musher to tears, and ended dozens of races through the years.

Measured against the fastest race in Iditarod history, Martin Buser's 2002 victory, this Iditarod is flying.

Need proof?

• In 2002, eventual race champion Buser reached Rohn at 7:25 p.m. on Monday and left at 1:19 a.m. on Tuesday.

• This year, Mackey pulled in at 5:45 p.m. and left at 6:02 p.m.

Of course, the racers are only about 200 miles into an 1,000-mile marathon. Weather, health and a million other mishaps can happen before Nome, but the combination of ideal weather and excellent snow conditions appear to be delivering a bounty of speed for the frontrunners.

"Boy, they're rolling," said Willow veteran Linwood Fiedler, who's sitting out this year's race with an injury. During Buser's record run, Fiedler was the first musher out of Rohn, nearly an hour ahead of Buser. He ended up scratching in Ruby.

Just a few days ago, Fielder was on the Susitna River headed toward Skwenta on a snowmachine.

"I've never see that river so flat -- so hard and fast," he said. "Usually you're fighting snow-go bumps and maybe some drifting.

"It's been cold at night setting up the trail and warmer during the day. My guess is that it's just wind-blown and hard.

"Remember, though," he cautioned, "it's a long ways to Nome."

And a lot of racers want to get there first.

By 8 p.m., a growing crowd of 10 mushers were in Rohn. Among them were past champions (Buser), runners-up (Hans Gatt, Sebastian Schnuelle and Paul Gebhardt) and a couple of surprises.

Anchorage's Robert Bundtzen, 61, who's never finished higher than 27th in a dozen Iditarod races, was running fourth with all 16 of his dogs in harness. And Bruce Linton of Kasilof, who's never been higher than 25th was 10th.

Linton, a Type 1 diabetic, has also race three Ironman triathlons and aims to spread the message that diabetics can accomplish an array of athletic feats. His kennel, the No Limits Sled Dog Kennel, is the first hint.

His team of speedy dogs is the second.

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Reach reporter Mike Campbell at mcampbell@adn.com or 257-4329