The Team Sky man proved too good for rising star Eddie Dunbar (Axeon Hagens Berman) and Ryan Mullen (Cannondale) at the end of a close-fought battle on the 40-kilometre course from Kilcullen to Athy and back.
Mullen was looking for back-to-back elite national and U23 titles but can have no complaints on the night, though his crash at the ZLM Toer in the Netherlands last weekend was perhaps a factor in his below-par result.
Roche stopped the clock at 47:14 and at the time of going to print, Dunbar’s time had not been made official, though it was faster than the 48:39 that Mullen clocked.
It’s a brilliant result for Roche who made no secret of his desire to win last night and because of that he will wear a specially-made jersey for the the next 12 months.
He last won the championships way back in 2007 and based on this form he will be hard to bet against in the road race on Sunday.
Yesterday, he was overlooked for selection by his team for the Tour de France for the first time since 2008 but he put that disappointment to one side last night.
Dunbar, a runner-up last year, put up a massive fight in a bid to win and he should be very content with the silver medal, given the quality of rider he was beaten by in Roche.
The women’s event was won by the little known Anna Turvey (Tyneside Vagabonds CC) in a time of 54: 28 - a staggering 3:20 ahead of runner-up Eve McCrystal (ASEA-Wheelworx) with Lydia Gurley (Aerocoach) next at 58:12.
Turvey declared for Ireland in the last 12 months having previously represented Scotland.
She rode the British time-trial championships last year and finished 17th but has since switched her allegiance to Ireland.
She rode the Commonwealth Games in 2014 for Scotland and is a former British duathlon champion.
She recently smashed the British 25-mile record so perhaps it was always a race for second last night.
The championships take a break today but tomorrow sees the Masters over-40, 50 and 60 events as well as the separate women’s race take place.
Aidan Crowley (Strata3/VeloRevolution) is the defending over-40s champion but with a field upwards of 170 for it, it will be a wide open race.
Lydia Boylan (Team WNT) is hard to look beyond in the women’s race but can expect a huge challenge from the likes of McCrystal and Turvey.