The native of Canmore, Alta., won the men's visually impaired 20-kilometre race in a time of 52 minutes 37.1 seconds for his eighth career Paralympic gold medal.
Russia's Stanislav Chokhlaev was second, 1:16.0 back, while Sweden's Zebastian Modin finish third, 4:33.3 off the pace.
McKeever won three gold medals at the Vancouver Paralympics four years ago and has two more races to go at the Sochi Games.
On Monday, he took a chance by starting with guide Erik Carleton before switching to alternate Graham Nishikawa at the 10-kilometre mark.
"Today was great," said McKeever, who has been fighting a virus for the past week. "It was really tough. Being sick last week made it hard and definitely made us a little nervous. It was huge team effort having two guides out there sharing the work. It was definitely needed. They were the ones that got me through today because I couldn't have done that on my own."
Brittany Hudak of Prince Albert, Sask., was 10th in the women's 15-kilometre classic-ski standing race. Ottawa's Margarita Gourbounova and Regina-based guide Andrea Bundon were fourth in the women's 15-kilometre visually impaired category.
After Monday's competition, Canada was fourth in overall medals with six (1 gold, 2 silver, 3 bronze) while Russia led the tally with 24 (7-10-7).
Elsewhere Monday, Canada's wheelchair curling team had its first loss of the Games after opening the day with a 7-2 win over the U.S. and then losing 8-6 to Norway in the afternoon.
"We were just on the wrong side of the inch on the last half of the game," Canadian skip Jim Armstrong said of the Norway loss. "It's round-robin, and all we've got to do is be here on the weekend (during the medal round). That's when it matters."
Canada is now tied with Russia atop the standings at 4-1.
Calgary's Alexandra Starker was the top Canadian in alpine skiing, finishing seventh in the women's standing division with a time of one minute 36.52 seconds. Alana Ramsay of Calgary was 10th in 1:43.39 while Toronto's Erin Latimer didn't finish her run.