The tourists, still to win a single match on tour, collapsed to be all out for just 206 then captured just two wickets in reply as NSW wrapped up victory with eight overs to spare.
But Irani, who was hit for three sixes in his final over after top scoring with 81, said England were confident they could find their form by the time the one-day internationals begin next week.
"It's disappointing, there's no doubt about it, but you must play these games with a purpose to improve yourself," Irani said.
"Of course we've got to get a result under our belt, there's no doubt about that, but you've got to get something out of the game as an individual before you go into the big ones, that's when it counts."
Unwanted Australian Test batsman Michael Slater, who made 115 off 136 balls to steer NSW to a convincing victory at the Sydney Cricket Ground, agreed with Irani that the result was irrelevant.
"A few of the English lads have come in to join this one-day squad and haven't had a lot of cricket recently so this was a much needed outing for them," Slater said.
"And fortunately for England it's not the competition they're here for so they'll take a lot out of this game."
While Slater put the result beyond doubt with his dashing hundred, it was Michael Bevan and Steve Waugh who guided NSW past England's dismal effort.
Bevan finished not out 54 while Waugh belted an unbeaten 24 off just 14 balls including three sixes in the final over to seal victory.
England failed to mount any challenge after collapsing to be all out in 49.2 overs when they lost their last five wickets for 18 runs.
Irani made a patient 81 and Nasser Hussain (34), Owais Shah (24) and Ian Blackwell (29 not out)
Irani and Hussain added 79 for the third wicket after openers Marcus Trescothick and Nick Knight both departed cheaply but three quick wickets from part-time spinner Simon Katich put the brakes on England's recovery.
When Irani finally departed after an innings spanning 140 minutes and featuring 11 fours, the lower-order quickly crumbled leaving NSW chasing a modest total for victory.
Slater, dropped from the Test team during last year's Ashes tour in England, was not even included in the original NSW team but got a last-minute call-up when Mark Waugh pulled out with a groin strain.
Never one to miss an opportunity, the right-hander responded with a dashing display that included 13 boundaries and a six.
He whacked 18 runs off one over from Andy Flintoff to reach his half-century off 53 balls then brought up his second one-day hundred off 119 balls in 136 minutes, reaching triple figures with a lofted drive off Ian Blackwell that went for four.
He was dismissed with the total on 182 when he was brilliantly caught by Trescothick at mid-wicket off Flintoff in what was England's last moment of joy on another miserable night.
Bevan, arguably the world's best one-day batsman, had shared a 134 run partnership with Slater after Corey Richards fell for seven.
The crafty left-hander brought up his half-century off 70 balls before Waugh chipped in with a big-hitting display at the death that included three sixes in five balls off Irani, the first landing in the upper deck of the member's stand and the third ended the game.
The match was England's first official one-day game of the tour. They are due to play Australia 'A' on Sunday and the Prime Minister's XI on Tuesday before the start of the triangular international series with Australia and Sri Lanka next week.