Yarnold, who was fastest in Friday's opening runs, maintained her dominance by completing the quickest times across all four for a combined time of 3 minutes, 49.95 seconds.
Yarnold beat Loelling, the German two-time junior world champion, by 0.67 seconds and Canada's Elizabeth Vathje by 0.79.
Vathje's bronze was Canada's eighth medal by a female skeleton athlete in the twelve world championships since 2000.
Another Canadian, Jane Channell, was fourth -- ahead of Germany's Tina Hermann.
Martins Dukurs won the men's title on Friday. It was the Latvian's third skeleton world championship title after wins in 2011 and 2012.
Anne O'Shea was the top American finisher in 18th place.
Dukurs, who also won the title in 2011 and 2012, beat the Russian by 0.69 seconds.
Tomass Dukurs took the bronze medal, 1.52 seconds behind his younger brother.
Earlier, Olympic champion Lizzy Yarnold of Britain took a slim lead midway through the women's competition.
After two of four heats, Elisabeth Vathje of Canada was 0.07 seconds behind.
Junior world champion Jacqueline Loelling of Germany and Jane Channell of Canada were tied for third, 0.39 seconds back, going into the final day of the competition on Saturday.
Germany's Tina Hermann is close behind in fifth, 0.52 seconds back.
Megan Henry and Annie O'Shea were the best American finishers at 17th and 19th place with two heats to go in the competition.
Dukurs was .17 seconds ahead of defending world champion Tretiakov after Thursday's two runs. Dukurs is the silver medalist from the 2010 and 2014 Olympics.
Dukurs' brother Tomass was in third place, .69 seconds behind the pace.
Matt Antoine, who won a surprising bronze medal at the 2014 Sochi Olympics, was the leading U.S. finisher, sitting in 11th overall. Teammate Kyle Tress sits at 15th.
"I thought we'd be more in the mix based on our training times this week," U.S. skeleton team head coach Tuffy Latour said in a statement. "Coming off an Olympic bronze medal, Matt is the top performer on the team, and he's put a lot of pressure on himself. We are three years out from the next Olympics, so if you're going to struggle, this is the year to struggle and work out the kinks. He's pushing himself to get better, and he's hungry for it."
The men's final two runs and the first two heats of the women's event are on Friday.
Information from The Associated Press was used in this report.
SOCHI, Russia -- Two American women with inspiring stories are both in medal contention halfway through the women's skeleton competition, setting up the possibility of an emotional finish Friday.
Noelle Pikus-Pace, 31, who retired after the Vancouver Olympics but returned in 2012 with the goal of winning her first Olympic medal, is in second place after her first two runs Thursday, .44 seconds behind Great Britain's Lizzy Yarnold.
Katie Uhlaender, who has battled injuries, concussions, depression and the death of her father, former Major Leaguer Ted Uhlaender, finds herself in fourth place after two runs, just .14 seconds from the podium.
"That would be a dream come true if Katie and I could both be up on that podium together, to have two U.S. flags flying and waving in the wind," Pikus-Pace said. "That would be absolutely incredible."
Pikus-Pace began the competition with an opening run of 58.68 seconds, breaking Uhlaender's year-old course record. That mark was short-lived, though, as Yarnold followed it up with a 58.43. Pikus-Pace corrected a few mistakes to turn in a second run of 58.65, solidifying her second-place standing.
Pikus-Pace, who finished fourth in 2010 in Vancouver, has sparked questions this week by taking only two of the available six official training runs. She is reportedly suffering from back issues.
"I'm just trying to take it a day at a time," Pikus-Pace said. "It's pretty hard when I only had a few runs here, but I felt well coming into the race today, although my first run was pretty sloppy to say the least. I feel happy with how I was able to come back in the second run and put it down. I know what I need to change tomorrow, and I'll be ready to give my best."
One of the final racers in the field, Uhlaender turned in a time of 58.83 in her first run, followed by a 58.75, the third-fastest time of the second heat.
"I'm having mixed feelings," Uhlaender said. "I was really happy with my first run even though I made some mistakes at the top that cost me quite a bit of speed, but the second run, I had a huge mistake at the bottom that cost me from pulling ahead."
While Sochi organizers have promised snow will be on the ground despite warm temps in the coastal town, one thing we can say for sure: The venues for the 2014 Winter Olympics will be there.
Here's a look at some of the locales you'll see next month:
The Shayba Arena will host ice hockey games and is in close proximity to other ice skating venues. Capacity: 7,000.
Fisht Olympic Stadium
The Olympic Stadium will host the opening and closing ceremonies, and most medal ceremonies. Capacity: 40,000.
'Ice Cube' Curling Center
You guessed it -- curling competitions will be held here. The venue is in the center of the "Coastal Cluster," where all of the ice-based venues are located. Capacity: 3,000.
Bolshoy Ice Dome
The ice hockey venue is said to be modeled after a "frozen water drop," but spectators may think it resembles a disco dance floor when they see the roof light up in multiple colors at night. Capacity: 12,000.
Skeleton athlete Zach Lund is taking a break from the sport but still hopes to compete in the 2014 Winter Games in Sochi, Russia, USA Bobsled and Skeleton announced Friday.
"I still hope to compete in the next Games," Lund said in a statement. "If I'm going to have any chance of doing that I need a break both mentally and physically. Once I started sliding this season, I realized I needed to take at least a year off."
Lund cited spending more time with his wife and daughter and a lack of passion as his reasons for taking the leave of absence.
"Maybe I'll get a second wind, maybe I won't," Lund said. "I see guys like Matt Antoine and John Daly who are hungry and passionate, and they really want it. Here I am on the opposite side of the spectrum, and that's not a good situation. I thought that the pressure would be off my shoulders this season and I could relax and enjoy sliding again, but I struggled doing that."
Lund made his first Olympic appearance in Vancouver, finishing in fifth place overall in the skeleton race.
In 2002, he suffered a debilitating car accident after being rear-ended and was removed from the Olympics.
In 2006, Lund was the top-ranked skeleton athlete in the world. He was notified an hour before the opening ceremonies that he was removed from the U.S. Olympic team for testing positive for Propecia, the hair restoration drug. The International Olympic Committee removed Propecia from the banned substance list in 2007.
"Sometimes I think about what I missed out on in 2006, and as much as I've been able to cope with it, it still gets me deep down inside," Lund said. "It took the passion and drive out of me and was a huge blow to my career."