Maharoof's haul of four for 25 in 10 overs included a sensational start that saw the pace bowler take three wickets in four balls in his first over.
Off-spinner Muralitharan followed up with two wickets in three balls in his first over on his way to a miserly return of four for 19 in five overs.
Sri Lanka needed just 10 overs to reach their victory target of 78 with Sanath Jayasuriya 24 not out and captain Mahela Jayawardene 39 not out, their team winning with 40 overs to spare, in what was both sides final Super Eights match.
It was another tough day for Ireland, shock conquerors of Pakistan, after they were dismissed for 91 by champions Australia earlier in the Super Eights.
Ireland's total Wednesday - which featured five noughts - was the lowest at this World Cup, edging Bermuda's 78 against Sri Lanka.
The 1996 champions recalled bowlers Chaminda Vaas and Muralitharan, controversially rested for the seven-wicket defeat by world champions Australia here Monday when they were already through to the semi-finals, but it was Maharoof who sparked the slide.
The first change was pulled and driven through extra-cover for fours off his first two balls by left-hander Jeremy Bray.
However, he then switched to round the wicket, and with his next delivery had Bray pushing a catch to Russel Arnold at short extra-cover leaving Ireland 28 for one in the eighth over.
Two balls later Andre Botha sparred outside off-stump and was caught behind by wicket-keeper Kumar Sangakkara for nought.
Next ball Eoin Morgan was brilliantly caught by a diving Sangakkara for a golden duck and Ireland were 28 for three with Maharoof on a hat-trick at the start of his second over which Niall O'Brien survived.
But Maharoof had a fourth wicket when opener William Porterfield (17) skied to Jayasuriya at mid-on.
Murali then struck with his second ball when Niall O'Brien was caught behind and two balls later postman Kenny Carroll, on his World Cup debut and the only change to the team that beat Bangladesh by 74 runs in Barbados on Sunday, was bowled round his legs for nought.
Maharoof then ran out Ireland captain Trent Johnston for nought.
Kevin O'Brien and Kyle McCallan both fell cheaply to Muralitharan before Dave Langford-Smith, dropped on four, hit Maharoof for six.
Langford-Smith was last man out, lbw to Vaas for 18, the innings finished inside 28 overs.
Ireland quick Boyd Rankin struck with his sixth ball when Upul Tharanga was well held at backward point by Porterfield, leaving Sri Lanka one for one.
Carroll then held a sharp catch at extra-cover to dismiss Sangakkara (10) off Langford-Smith but 25 for two was as good as it got for Ireland.
This was Ireland's final match of the World Cup, the surpise package of the tournament starting the day seventh in the standings and unable to qualify for the semi-finals.
Their score was compiled against a Sri Lanka attack missing fast bowler Lasith Malinga, out for a third straight game with a left ankle injury.
Sri Lanka's next match is the first semi-final in Jamaica on Tuesday where their likely opponents will be New Zealand.