Eoin Morgan and Ravi Bopara hit centuries to guide England to a six-wicket win over Ireland in Dublin, the city of stand-in captain Morgan's birth.
Morgan and Bopara put on a one-day international record 226 for the fifth wicket as England recovered from 48-4 to chase down a target of 270 with 42 balls to spare in the one-off fixture.
Morgan, who played 23 ODIs for Ireland before switching allegiance, finished on 124 not out from 106 deliveries, his fifth ODI hundred, while Bopara's 75-ball 101 not out - his maiden ODI century - featured 10 fours and five sixes.
Their partnership rescued England from early trouble after Tim Murtagh (3-33) claimed three wickets in his opening spell.
Trent Johnston (1-34) removed Michael Carberry - making his England ODI debut along with Gary Ballance - lbw for 10 to start the collapse.
And Murtagh, the London-born Middlesex seamer who qualifies for Ireland via his grandfather, removed Luke Wright (5) and Ballance (0) in the ninth over to leave England wobbling on 25-3.
It was approaching a full-scale crisis when James Taylor soon followed, bowled by Murtagh for 25.
But Morgan and Bopara thwarted Ireland's hopes of a second ODI win over England to go with their success at the last World Cup.
The required-rate was quickly brought under control and both batsmen finished the match in a flurry of strokes.
Morgan struck eight fours and four sixes but it was Bopara who caught the eye in the closing stages, bringing up his century with a sequence of four, four, six, four before completing England's task with a single.
Ireland captain William Porterfield's 112 had earlier led his side to 269-7 after they had been asked to bat at Malahide, which became the 185th venue to host a one-day international.
Opening batsman Porterfield struck 14 fours and a six in his 142-ball knock and was given good support all the way down the order with the O'Brien brothers, Niall and Kevin, John Mooney and debutant Max Sorensen all chipping in with 20s.
Another of England's former Ireland players, Boyd Rankin, claimed 4-46 on his first ODI appearance for his adopted country.
His haul included Ed Joyce, who he had also dismissed at the 2007 World Cup, albeit on that occasion Rankin was playing for Ireland and Joyce opening the batting for England.