The 30-year-old all-rounder, whose return surpassed his previous ODI best of 4-34 against Sri Lanka in Cardiff in 2016, also told Sky Sports: "I wasn't sure whether my opportunity would come again, I absolutely loved being out there, wearing the "Three Lions" again, and wickets are just a bonus".
Speaking ahead of the match, England captain Eoin Morgan refused to take Ireland, his former team, lightly.
The three-match series in Southampton kick-starts the ICC Men's Cricket World Cup Super League, which will serve as the qualification process for the 2023 World Cup.
Campher, a South African-born all-rounder who qualifies for Ireland through his mother's passport, showed admirable fortitude on his first worldwide outing, surviving a hat-trick ball before going on to share stands of 51 and 66 with Kevin O'Brien and Andy McBrine.
Together with Andy McBrine (40) he shared a stand of 66 after Ireland were in danger of being dismissed for under 100 at 79-7.
Willey had a second wicket with just his seventh delivery, the left-armer getting a delivery to hold its line as Ireland captain Andrew Balbirnie's wild slash took a faint nick before being caught behind.
Next ball, the 30-year-old Willey, the son of former Englandbatsman and umpire David Willey, had Lorcan Tucker lbw for a duck to leave Ireland 28-5.
The 21-year-old former South Africa youth global, qualified for Ireland through his mother, went on to an admirable 103-ball fifty.
When will the England vs Ireland 1st ODI begin?
The players on both sides took a knee in support of Black Lives Matter - as was the case during England's Test series against the West Indies - before Willey made inroads into the batting line-up with just his fourth delivery.
England's red and white-ball fixtures are overlapping in a season cut short by the coronavirus outbreak and they are maintaining two separate squads, meaning a clutch of World Cup winners including Joe Root and Ben Stokes will not feature against Ireland.