Britain's Katie Archibald won gold in the women's omnium at the Track Cycling World Championships in Hong Kong.
The 23-year-old Scot held off Australia's Amy Cure in the points race for her first individual world title.
World Championship debutant Ryan Owens reached the quarter-finals of the men's sprint as fellow Briton and Olympic champion Callum Skinner crashed out.
Archibald won Olympic gold alongside Barker, Laura Kenny and Joanna Rowsell Shand in the team pursuit at Rio 2016 and was world team pursuit champion in 2014.
But with defending world and Olympic omnium champion Kenny pregnant with her first child, Archibald was handed an individual spot and seized her opportunity.
"I feel really privileged to pull it off," she said. "It was an unbelievably grippy race, I really thought I'd lost it in the middle point but I pulled it out of the bag.
"It feels very strange, I'm used to having my girls, my team-mates, around me it's odd to celebrate by yourself but I'm looking forward to catching up with them at the hotel."
European champion Archibald won the first two events - the scratch race and the newly-added tempo race - and led by eight points at the halfway stage.
She finished fifth in elimination race as rival Cure took maximum points, meaning the two were level going into the final event.
Archibald edged two points clear before the final sprint of the points race, and put in a fantastic push down the final straight to secure victory.
It was her first individual success on a world stage and she has had to overcome multiple setbacks on her road to individual glory.
At the end of 2015, a motorbike accident forced her to withdraw from the 2016 World Championships in London and she was heavily criticised by ex-British Cycling technical director Shane Sutton.
In November last year, she fractured her wrist as she partnered Manon Lloyd to victory in the inaugural women's madison at the Track Cycling World Cup in Glasgow.
Olympic gold medallist Chris Boardman
A wonderful performance. I thought she was completely spent in the closing stages; I genuinely didn't think that she had another sprint in her. But she just found something from somewhere to take the sprint from her rivals.
She knew she only had one effort, Cure went too early but nobody could manage the speed of Archibald's final dash.
Eleven-time world gold medallist Sir Chris Hoy
Some of the big names are out of the British team but it's giving the younger riders a chance to shine and hopefully cement a place in the team come Tokyo 2020.
'I can't be too disappointed'
Earlier, Owens eased into Saturday's quarter-finals of the men's sprint. The 21-year-old, who travelled to Rio 2016 as a reserve, beat Hugo Barrette of Canada.
But individual sprint Olympic silver medallist Skinner suffered a second-round exit.
The 24-year-old Scot, who also won Olympic gold in the team sprint alongside Kenny and Phil Hindes in Rio, was beaten by Max Niederleg of Germany.
"The field were three or fourth tenths ahead of my pace and it makes it difficult when you come up against the second seed," Skinner told BBC TV.
"It's just a reflection of where we are. I can't be too disappointed."
In the men's individual pursuit, Matt Bostock and Andy Tennant finished 13th and 14th while, in the men's points race, Mark Stewart came seventh.