Canada's two other entries are inside the top 10 at Alpensia Sliding Centre. AlysiaRissling and Heather Moyse occupy seventh spot (1:41.76) while Christine de Bruin and Melissa Lotholz are eighth (1:41.85).
Helen Upperton, who was the first Canadian woman to win a World Cup bobsleigh race in the 2005-06 season, wondered if Humphries's slow start is related to equipment.
"[Her] driving is pretty good, so it could be a runner choice," said the retired bobsledder-turned CBC Sports analyst. "They [athletes] have a few sets to choose from, based on the weather, and Kaillie may have picked the wrong set of steel.
"She doesn't love this track. She struggled here in the Olympic test last year. It was the only time she was beaten by another Canadian [Rissling with a bronze]."
Coming off her fourth overall World Cup season title in five years, Humphries appeared slow at the bottom of the course in her second run and lost a lot of time, finishing in 50.88 seconds after briefly setting a track record of 50.72 in the first run.
"Keep in mind, there are four heats [in the Olympic competition]. Consistency is extremely important," said Upperton, a 2010 Olympic silver medallist who retired two years later with six victories and 20 podium finishes."
George, whom Humphries recruited after her top-10 finishes in hurdles and 4x100-metre relay at the 2016 Rio Summer Olympics, had a strong push and good load in a fairly clean first run.
Record 48 World Cup medals
Humphries, who has piloted her sled to a record 48 career World Cup medals, had George on her sled for the final four races this season, winning gold and silver. She also split time with Lotholz, who has pushed Humphries to six of her victories and 15 World Cup podiums.
Humphries won gold at the 2010 Vancouver Olympics with Moyse as her brakeman and four years later in Sochi, Russia, they beat American Elana Meyers Taylor by 1-10th of a second for top spot. On Tuesday, Meyers Taylor set a start record of 5.21 seconds and sits second (1:41.33) to Germany's Mariama Jamanka and Lisa Buckwitz (1:41.26).
The United States is the only team that has medalled in all five Olympic Games since women's bobsleigh debuted in 2002 at Salt Lake City. Meyers Taylor was a push athlete in Vancouver and returned as a driver in Sochi, winning a silver medal.
Moyse, 39, came of retirement last September to serve as brakeman for the 29-year-old Rissling, a former basketball player at the University of Alberta. Rissling made up for some big mistakes in her second run but de Bruin, making her Olympic debut, and Lotholz closed the gap with a 50.91-second performance to set up a good battle for Wednesday.
"A good run by Christine," said Upperton. "She's come back from a lot of adversity … a bulging disc in her back [in 2014] that affected her sciatic nerve."
Run 3 is scheduled for Wednesday at 6:40 a.m. ET and the final at 8 a.m.