Imagine sitting down to have your breakfast, expecting a nice quiet day, before being told you are making your international debut that afternoon against one of the world's top sides.

Paterson, called upon after Kyle Steyn's wife went into labour, made just his ninth professional appearance and only his seventh start, and went from a state of panic to delivering what head coach Gregor Townsend described as "one of the best debuts I've ever seen".

For someone so young and inexperienced, one can only imagine his emotional rollercoaster when Townsend told him the news.

"I kind of figured what would be happening when I got the phone call," Paterson said.

"There was about 5-10 minutes of panic, but then I stabilised a bit and cooled down. But I was really excited. Nerves obviously, but I was really looking forward to it.

"It was whenever I thought of my dad I had to control things a wee bit, and think about the job at hand first and deal with the emotional stuff after."

Come kick-off though, Paterson took to Test rugby like a duck to water in a frenzied contest that concluded with Scotland controversially denied victory by an inconclusive last-gasp try review.

The Edinburgh youngster was rock solid at full-back and played a key role in the game's opening try. He burst away down the right wing before offloading superbly to Huw Jones, who in turn found scorer Ben White.

"I just kind of went for it, reminded myself to keep working hard," Paterson added humbly. "I can't rely on my pace like Duhan [van der Merwe], so I just charge about the pitch, chuck myself into as much as I can and hope that helps the team.

"I've been told I overthink a lot, but when it comes to game time I manage to chill out and not stress as much, really focus on enjoying things.

"Boys were saying beforehand, it's just another game of rugby, but it's also your first cap - make sure you enjoy it. Once you get playing, it's no different - a bit faster and more physical - but that settled me.

"I was alright once I was out there. I got minced off the first ball I got, so that got me into the game and settled me a bit."

Townsend was effusive in his praise for the rookie full-back, who he trusted to step up in his natural position instead of selecting a makeshift full-back with more experience.

"It's one of the best debuts I've ever seen," he said. "Going up against that French backline on a wet day at Murrayfield, he was excellent.

"I gave him a heads-up that he could be playing about 9am, then confirmed it at 10am.

"To play like that was fantastic and gives us a lot of encouragement about where Harry can go over these next few years.

"He knew he'd have a lot of kicks to field due to the way France play and with the weather being wet, but he just got stronger and stronger as the game went on."

Just being in Scotland's Six Nations squad seemed a world away at the start of this season, but Blair Kinghorn's move to Toulouse and a couple of injuries gave Paterson his chance at Edinburgh, and he seized it with both hands.

The result, and the nature of it, made it a day of mixed emotions for Paterson, but he certainly isn't getting carried away after his impressive debut.

"Confused at the end of the game," he said. "I didn't really know how to feel, it was just gutting.

"The team manager managed to sort me out with tickets for my pals and my family. It was really nice to see them after the game, celebrate a wee bit but obviously it's a bit mixed.

"I've not played an awful lot of pro rugby, so now I need to build that base of games, stay fit and just crack on."