Attempting a mammoth blow to reach his century, Jacks slog swept to Andy Balbirnie at deep midwicket to depart for 94 off 88 balls for England, who are resting all their World Cup stars for this Metro Bank series.
Jacks thumped seven fours and four sixes but his downfall – one of three scalps claimed by George Dockrell – threatened to derail England and while Hain, one of four debutants, could not match his team-mate for power, the Warwickshire batter’s 89 off 82 balls proved vital in the hosts passing 300.
Ireland are seeking a third successive white-ball win over England – having beaten them in an ODI in 2020 and at last year’s T20 World Cup – and may fancy their chances after restricting their opponents to just 140 in the last 20 overs.
England got off to a flyer thanks to Jacks and Phil Salt (28 off 21 balls) while Ben Duckett contributed 48. A trademark onslaught in the latter stages was not forthcoming but Hain’s knock potentially opens the door for more regular involvement after the World Cup, which starts next month.
Hain started alongside Jamie Smith and bowlers Tom Hartley and George Scrimshaw, with the latter pair able to put their feet up after Ireland chose to field.
Jacks and Salt have been tipped to be the new Jason Roy and Alex Hales and the next generation gave their finest impression of the old guard, feasting on Ireland’s fruitless pursuit of early swing with a rash of fours.
Jacks was imperious against Josh Little, driving sumptuously through the off-side time and again, as England reached their 50 inside six overs before being dealt a double when Salt spliced to extra cover while, two legal balls later, stand-in captain Zak Crawley played all around one from Craig Young.
Duckett pierced cover on a couple of occasions and Ireland took out a lone slip, only for the luckless Barry McCarthy to twice draw the outside edge, desperately out of reach of wicketkeeper Lorcan Tucker.
Jacks was put down on 44 low at backward point by Harry Tector, who could not get under the chance. It was a costly, if extremely difficult, drop as Jacks went through the gears, bringing up his maiden international 50 with a lofted drive off spinner Andy McBrine for six.
Duckett also cleared the rope off McBrine but perished for 48 after paddling Dockrell into the inviting hands of Mark Adair at short fine-leg to end a run-a-ball 102-run stand with Jacks.
Hain made a nervous start with just a single – via an inside edge – off his first dozen deliveries and was put down by a diving Tector before gradually finding his stride, using his feet well to open up his scoring options.
Jacks moved into the 90s by hoicking Dockrell for six but, attempting to repeat the trick in the next over, he gave McBrine a skier. As he trudged off, Jacks knocked his bat into his helmet in despair.
Dockrell had his third when Smith holed out but Hain – who possesses one of the best List A averages ever – used his experience to make sure England did not collapse. While there were only five fours, he was able to rotate the strike sufficiently to reach a half-century off just 52 balls.
Brydon Carse made a cameo 32 off 30 balls and while Hain headed into the last over needing 11 to reach three figures, he miscued McCarthy to mid-off.