The fledgling centre-back feels performing in such circumstances shows he’s able to cope under pressure.
Casey spent a large section of last season on loan at Privett Park.
Borough were involved in a scrap at the bottom of the Southern League premier division south.
The fight for survival went right down to the wire, with Craig MacAllister’s side’s 2-2 draw with Metropolitan Police on the final day of the campaign maintaining their status in the division.
Casey was determined not to have a relegation on his C.V at just 19.
And the defender highlighted he can perform when the heat is on.
Casey said: ‘It was the most nerve-racking game I’ve ever played – even more so than my Pompey debut.
‘I didn’t get a lot of sleep the night before so luckily it went well. At such a young age, you don't really want a relegation on your C.V.
‘We did not want to lose that game because if we did then we knew we were down. Luckily we came out with the right result.
‘We'd won the second-last game of the season but mathematically weren’t safe so it was a tough last few weeks there.
‘It shows from a young age that I can handle pressure and do well, so hopefully I can keep progressing and keep getting better.
‘Macca and Tubbsy (Matt Tubbs) believed in me at Gosport and I was always on the pitch.
‘That was a good period for me and helped me the most for my development.’
Casey also spent time at Weymouth and Basingstoke last term.
At the former, he was limited to few opportunities, while he only featured once for the Dragons.
Casey added: ‘I didn’t really get a look in at Weymouth. They were looking for more experience because they were contending for promotion.
‘Centre-back is one of the hardest positions for young players and all managers like experience there.
‘I knew I could do it but it was getting that opportunity.
‘I played once for Basingstoke and the plan was to stay for longer but the gaffer needed me at Pompey.’