Dustin Britton, a 32-year-old mechanic and ex-Marine from Windsor, Colorado, said he was alone cutting firewood about 100 feet from his campsite in the Shoshone National Forest when he saw the 100-pound lion staring at him from some bushes.
The 6-foot tall, 170 pound Britton said he raised his chain saw and met the lion head-on as it pounced - a collision he described as feeling like a grown man running directly into him.
"It batted me three or four times with its front paws and as quick as I hit it with that saw, it just turned away," he said in a telephone interview with The Associated Press.
Wildlife officials said Sunday evening's attack about near Cody was highly unusual because mountain lions are reclusive by nature. Only eight cases of mountain lions acting aggressively toward humans have been documented in Wyoming over the last decade.
"It's very, very rare" for lions to attack, said Wyoming Game and Fish spokesman Warren Mischke. "We're still trying to investigate why this lion would behave this way."
The wounded animal retreated after Britton inflicted a six-inch to eight-inch gash on the lion's shoulder, leaving him with only a small puncture wound on his forearm.
The mountain lion was shot and killed Monday after it attacked a dog brought in to track the animal, which was 4 to 5 years old. Authorities say it was in poor physical condition and appeared to be starving.
After Britton's confrontation, he and his wife, Kirsta, decided to spend the night in their pop-up camper with their two children rather than risk packing up with the lion still on the loose.
Wildlife agents were called the next morning after Britton told a passing U.S. Forest Service employee about the incident.
Tests for rabies and other diseases came up negative, but officials said they were continuing to analyze the animal for other potential diseases.