Collingwood hit an 82-ball 90 to help England overcome early wobbles to put up a respectable 266-7 in their allotted 50 overs after electing to bat at the Guyana National Stadium.
Flintoff then grabbed 4-43 as Ireland found the going tough against the English attack and managed 218 in 48.1 overs with Niall O'Brien fighting a lone hand with a gritty 63.
England, who were without any carry over points, achieved their desired result and now face Sri Lanka at Antigua on April 4, while Ireland, who upset Pakistan to reach the second round, gave a good account of themselves despite losing.
Chasing a formidable target, Ireland lost opener Jeremy Bray (nought) and Eoin Morgan (two) early in their innings before Niall O'Brien added 61 for the third wicket with William Porterfield (31) to raise some hope for their team.
Niall O'Brien then put on another 44 for the fourth wicket with Andre Botha (18) before left-arm spinner Monty Panesar derailed the innings by dismissing Botha and then Kevin O'Brien (12) to finish with 2-31 off his ten overs.
Niall O'Brien fell soon after, stumped off English skipper Michael Vaughan to quash any outside hopes of a famous win. He hit fours during his 88-ball knock.
Ireland skipper Trent Johnston (27) and Andrew White (38) did try to hit out but their efforts were too late and too little.
Earlier, it was Collingwood who resurrected England's innings.
He added an invaluable 81 runs for the fourth wicket with Flintoff (43) to lift England from a precarious 113-4.
The 30-year-old Collingwood kept one end intact and hit eight boundaries and three sixes during his stubborn knock before he was finally run out in the last over.
Collingwood's knock came after England lost opener Ed Joyce (one), and Vaughan (six) as early as the sixth over.
Ireland were given a good start by their lanky paceman Boyd Rankin who surprised Joyce, a former Irish international, with a sharp incoming delivery which hit the off-stump in the second over before forcing an edge off Vaughan to wicket-keeper Niall O'Brien.
The 6ft 7in fast bowler finished with 2-28 off his seven overs.
Kevin Pietersen hit three boundaries off Johnston's opening over as he and Ian Bell (31) steadied the innings during their 66-run stand for the third wicket.
When it seemed Pietersen would put together a big score, he was smartly snapped up at mid-wicket by William Porterfield off Kyle McCallan.
Pietersen, the new world number one batsman, hit five boundaries during his 47-ball 48.
Flintoff, who failed to score in England's first round defeat against New Zealand and was dropped from the team over late night drinking for the Canada match, looked threatening as he hit a boundary off the first ball he faced.
But the Irish bowlers kept a tight line and length and never allowed Flintoff to hit out. Flintoff finally chopped Johnston onto his stumps after hitting four boundaries during his 62-ball knock.
Collingwood, who realised the importance of slog overs, reached his fifty off 65 deliveries and then cut loose, adding a quickfire 51 for the sixth wicket with Paul Nixon, who scored 19.