Replacements: Daniel Montgomery, Gavin Ryan, John Moroney, Sean Upton, Darren Ryan.
Replacements: Cian Culleton, David Hegarty, Tom Byrne, Ronan Dillon, Timmy McCoy.
On a pitch that was a credit to the Young Munster ground staff, it seemed as if their efforts might bring a big reward when goal-kicking scrum half Brian Haugh put them in front with a penalty after only three minutes.
The lead lasted only three minutes when a penalty from 'Tarf number 10 David Joyce punished Young Munster for being offside, and he put his side in front midway through the half.
A scrum infringement after 34 minutes cost Young Munster another three points when Joyce was again on target.
Just as he did in the first half, Haugh landed an early penalty in the second period but a try by his opposite number Sam Cronin after 63 minutes put a bit of daylight between the sides.
Another Haugh penalty brought the Limerick men back into contention. However, when a Young Munster player went in at the rong side to bring down a maul it yielded a decisive penalty try for the league leaders.
The north Dubliners mustered a third try two minutes from the end, as man-of-the-match and the division's top scorer Joyce made use of a quick turnover to complete his 16-point tally.
The result means 'Tarf are now three points clear of second-placed Old Belvedere at the summit, with Cork Constitution the visitors to Castle Avenue next Saturday.
Speaking afterwards, Clontarf head coach Andy Wood told the Irish Examiner: "Young Munster were dogged, determined and put us through the ringer at times. We're just delighted to get out of here with the win.
"We took our chances eventually. We got the win after a heck of a lot of hard work.
"There's a long way to go (in the league), still eight games to go. We'll take any amount of daylight we get but nothing's done yet.
"It's still (only) the end of January but If we work as hard as this and bring some accuracy then hopefully we'll get into our stride again."
Referee: Dudley Phillips (IRFU)