Plapp took the lead with his powerful ride over the 27.8km course, but was ejected from the hot seat when Evenepoel steamed home to take the title by 1:24 from Plapp, with Italy's Andrea Piccolo a further 14 seconds back in third place.
While Evenepoel, who will join the Quick-Step Floors team in 2019, has had an almost faultless season, Plapp can be extremely happy with a year that has included winning the Australian junior time trial championships and taking the junior TT title at the Oceania Championships, as well as two world titles at the junior track world championships in Switzerland last month, where he won both the Madison and the points race.
"I woke up so excited [on Tuesday], and just wanted to race and send it. 'No nerves, no hope,' I thought to myself when the butterflies started flying around," Plapp said on the Cycling Australia website.
"The course was crazy. It had a little bit of everything – so many climbs and so many descents.
"I wasn't sure how to feel about my time crossing the line. I was confident my time would be up there, but little did I know how much it would get beaten by," he said.
Plapp's time trial position – with his hands 'piled' on top of each other, reminiscent of British 2012 Tour de France winner and five-time Olympic champion Bradley Wiggins' TT position in later years – helped carry him to his second place, and the 17-year-old from Melbourne finished knowing he had put everything into his ride.
"I'm pretty stoked with the silver, and it has been an unreal couple of months," said Plapp, referring to his world titles on the track.
"It's a bittersweet feeling. 'Never put a number on to come second,'" he added, quoting his own approach to racing, "but there was nothing I could have done to get the top step."