Watts, along with Academy products Elias Sørensen, Matty Longstaff, Owen Bailey and Tom Allan, all made their senior debuts during United's Premier League Asia Trophy defeat to Wolverhampton Wanderers in Nanjing.
And after achieving a childhood dream of playing for Newcastle's first-team squad, the Alnwick-born centre-back positively recalled on his memories whilst in the Far East as the Magpies finished in third place after a 1-0 play-off victory over West Ham United in Shanghai.
The 19-year-old told nufc.co.uk: "I was told before the game that I would be coming on around 55-60 minutes. In football though, things can change so it was just about being ready. At half-time, I could sense it was nearing a bit closer and then when I warmed up with the senior lads before being told I'd be coming on.
"You sort of blank everything out. I couldn't even remember what my surroundings were of how full the stadium was. It was getting fuller and fuller but I couldn't really hear any noise as I was in the moment.
"The atmosphere was great and there was a lot of local supporters. The Manchester City-West Ham United game was on after our game so the stadium was beginning to fill gradually, especially when myself and the younger lads were coming on.
"The noise around the stadium was brilliant and coming on for my first game with Newcastle's senior team was a brilliant experience.
"Whilst playing alongside Fede (Fernández), he talked to me a lot and when I first came on, he told me to just play my normal game. Throughout the week, I'd been taking in lots of information from all of the first-team squad. It wasn't just from those in my position but in midfield too and what passes players liked to receive.
"Whether it was on the pitch or around the dinner table, I just listened to the bits of information. I know they are much more experienced and older than me and I just wanted to listen to them as they are at a level where I aspire to be at.
"I think being around men and playing men's football for that week was great as I was able to get used to the physicality. It is much more different. Players might have the height, build or have the same pace but the way the ball moves is so much quicker compared to under-23 level.
"Moving forward, I can hopefully, in the short time with the team, use that speed of thought more to try and stand out."
United's second-string continue their pre-season preparations, travelling to Rotherham United on Monday afternoon (kick-off 2pm BST) for their final fixture before the youngsters' Premier League 2 campaign commences in August.
And Watts believes his recent stint in China will benefit himself and the four youngsters who featured for United's first-team squad as the under-23 side aim to build on their positive season last term, reaching the Premier League Cup final and Premier League 2 division two play-off final.
Watts added: "It gives yourself massive confidence from travelling with the first-team squad because if you can play at senior level, you feel can go and play under-23 games.
"It's a massive difference in terms of levels and it should give the lads, who played in China, the belief in their own ability.
"It shows that the club think of highly of the players and going back to the under-23s after that experience abroad will help massively.
"A few of us that went away to China have only played 30 minutes of football. It will be good to hopefully play a large part of the game to get our fitness levels back up to our best.
"Being back with the lads who we done so well with together last season will be useful. Some of us have played with each other since a young age so, although it will be good to be back and play together before the start of the season, we all know each other's game, which is a big positive in our group. We all have been playing together for so long that it comes naturally."
