Stormont: A matter of hours after celebrating Test series success over Australia, they appeared on course for a comprehensive defeat with the Irish well set chasing a revised target of 116 in 20 overs.
They spectacularly lost to the Netherlands in the World Twenty20 in June but managed to hold out this time as a makeshift attack prospered on the sluggish surface.
Twice he cleared the ropes as he scored all but six of a 42-run stand with Adil Rashid, another of England's three ODI debutants.
Only a brilliant catch by John Mooney, who flung himself full length on the run from long-off, halted Wright's 26-ball assault.
That gave Johnston final figures of four for 26 in conditions perfect for his medium-fast repertoire and ones in which the Irish would have been confident of claiming their most famous scalp.
The minnows defeated both Pakistan and Bangladesh in the 2007 World Cup and knocked the Bangladeshis out of the World Twenty20 this summer.
Although they brought a full-strength squad to Stormont - minus captain Andrew Strauss - England left out leading players Stuart Broad and James Anderson, as well as Morgan, who played for the hosts the last time the sides met here three years ago.
The star of England's show was the debutant, Joe Denly, who opened the batting on a ground that holds many happy memories for him. He scored his maiden limited-overs hundred for Kent against Ireland in the Friends Provident Trophy in 2007, and he replicated that same composure to top-score with 67 from 111 balls.
The Man of the Match award, however, went to Johnston, who was playing in his 100th match for Ireland and seeking a measure of revenge for his mother country, Australia. He removed both Ravi Bopara and Jonathan Trott for ducks before Denly was even off the mark, and eventually finished with the impressive figures of 4 for 26.
England: 203 for 9 (Denly 67, Johnston 4-26)
Ireland: 112 for 9 (Shah 3-15)
Result: England won by three runs (D/L method)
Man of the Match: Trent Johnston (Ireland)