Swingley, from Lincoln, Mont., reached the finish line of the 1,100-mile sled dog race at 1:31 a.m.
He won in an unofficial time of 9 days, 14 hours and 31 minutes.
The triumph earned him $54,000 and a new pickup, to go along with $9,000 in bonus money he won on the trail.
More than seven hours back was Buser, who was the runner-up when Swingley won his first Iditarod in 1995. Buser, from Big Lake, left White Mountain at 11:07 p.m. Tuesday to cover the remaining 77 miles to this historic Gold Rush-era city.
Swingley's victory margin stands to be the widest since 1992, when Buser finished more than 10 hours ahead of runner-up Susan Butcher.
Swingley borrowed from a race strategy that worked for him in 1995 - go farther than the pack before taking his mandatory 24-hour rest, and then outrun everyone else to the Bering Sea coast.
He also caught a few big breaks. Injuries led Buser to cut his team from 16 dogs to 10 early in the race, which forced him to run a more conservative race. And after leaving the Yukon River, Swingley just missed a bout of bad weather that slowed other front-running teams.
Swingley also broke two sleds, but neither slowed him down. He patched the first with a stick and a few hose clamps. The second broke just before his 24-hour layover in Iditarod, leaving him plenty of time to fly in a replacement.
Rick Swenson of Two Rivers, a five-time Iditarod winner, was running third Wednesday. He was on the trail to White Mountain, having left Elim at 6:02 p.m.
A few hours behind Swenson were Vern Halter of Willow and Charlie Boulding of Manley. Four more Alaskans were a couple of hours farther back: John Baker of Kotzebue, Paul Gebhardt of Kasilof, defending champion Jeff King of Denali Park and Ed Iten of Kotzebue.
By T.A. Badger