The Belarusian looked on-song througout the 53km time trial around Richmond, Virginia even as the pre-race favourites struggled to find their best selves.
Kiryienka posted a winning time of 1hr 2min 29.45sec to finish nine seconds ahead of Adriano Malori (ITA) while Jerome Coppel (FRA) surprised in third at 29sec.
"Today was no surprise for me. I planned this with the help of my team, and it's great that I've beaten so many talented riders, Kiryienka said.
"I want to thank Team Sky. they have done an amazing job for me and I couldn't have done this without their support. I dedicate this win to them.
"I can't say how many days I've waited for this, and how many hours I've put in on the bike. There's so many things to consider in time trialling, so much work to do with the bike and the aerodynamics.
"Today it was a matter of finding my balance and setting a tempo, and I am happy I could get this win."
Australia's Rohan Dennis was a red-hot favourite to win the event but never looked at his best and finished sixth. He might have medalled, but a mechanical and bike change made the difference in keeping him off the podium.
Trouble on the road for Rohan Dennis @richmond2015 #sbscycling http://t.co/zDrdOMHnzQ — CyclingCentral (@CyclingCentral) September 23, 2015
“It started pretty well,” Dennis said. “I went out on my pace. I was little bit down on after the first two checkpoints but holding steady.
"With around 25 kilometres to go, I was going on the main highway and I got a rear puncture. Bit of a bummer, but it’s sort of the way it goes sometimes.
“I could try to blame that on the reason why I lost, but I wouldn’t have beaten Kiryienka anyway. He was on an awesome ride. Now I’m back to the drawing board to work on next year and Rio.”
“It is a bit of an average way to finish the season, but it’s been an exceptional season. I can take a lot of confidence out of what I have achieved.
"Today would have been the cherry on the top if I could have pulled it off, but my result today doesn’t take away from all that I’ve accomplished.”
Co-favourites Tom Dumoulin (NED) and three-time world champion Tony Martin (GER) suffered a similar medal fate to Dennis, with both riding cleanly but finishing fifth and seventh.
Australian Michael Hepburn was the first rider out of the start gates setting a fast time which stood until Steve Cummings (GBR) ended his ride.
“It was a hard race today,” Hepburn said. “The course was relentless. There wasn’t any place that you could back off.”
Heppy left it all out on the road in the @richmond2015 ITT #sbscycling http://t.co/7bU6esO9p1 — CyclingCentral (@CyclingCentral) September 23, 2015
Next to lead was Poland's Marcin Bialoblocki before Coppel then Malori replaced him at the top of the leaderboard.
Kiryienka quickly rode over Malori and only had a short wait for Martin to finish before his winning ride was confirmed.
"It was a really demanding TT, Malori said. "I felt pretty good, and the tailwinds on the opening eight kilometres made it even better.
"It was the perfect terrain for me, and I tried to keep that speed, yet saving some energy for the steep finale.
"Ending up seconds off the podium is awful of course, as it was quite a good opportunity, but it gives me much confidence for the near future."
SBS will broadcast the under 23 men's road race on Saturday 26 September from 3:00am AEST on SBS/HD with streaming available right here on the Cycling Central website.
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