When was the closest finish on the iditarod?

The closest finish was Dick Mackey over Rick Swenson in 1978. Mackey's time was 14 days, 18 hours, 52 minutes and 24 seconds. Swenson's time was 14 days, 18 hours, 52 minutes and 25 seconds... meaning that he missed being the only SIX-time winner of the I-rod by one second. He is still, however, the only FIVE-time champion.