The 20-year-old accomplished this landmark feat at Footes Lane yesterday, defying troublesome winds and the lack of lasting competition to clock an outstanding 49.87sec.
Chalmers lined up aiming to give it his all – and he truly did.
It became apparent that he needed a storming finish to hit the desired mark, and in the heat of the moment, he practically hurled himself across the line to anchor down the fastest 400m hurdles ever run on Guernsey soil.
After celebrating from a supine position and rising to hug his proud father, Chris, the youngster reflected on another great bound in his hurdling progression.
‘You’ve got to do everything you can to run these world-class times,’ said Chalmers.
‘It’s just a massive tick off the list.
‘When I came down today, I knew it would be hard because of the wind, and it’s just a local race – the first of the season in a way.
‘I knew I was in the shape to run sub-50 but to actually go out and do it is a different race.’
What’s next? Chalmers eyes several more local appearances, before joining the elite competing behind closed doors at the British Championships from 4-5 September.
Dale Garland’s outright Guernsey record of 49.54 is now under new pressure.
‘Imagine what I can do at the British Championships with pure competition and a normal day of wind,’ he added.