Munster moved five points clear at the top of Pool 1 in the Heineken Cup after they beat Scarlets 19-13 at Thomond Park on Sunday.
Ten points in the space of as many minutes at the start of the second half eased Munster ahead after the Scarlets had matched them for the first 40.
There was just a single Ronan O'Gara penalty between the two teams at the break and the Welsh region had been the more creative side without ever getting the points they needed.
The Scarlets hadn't beaten Munster in 14 straight games coming into the match, but their free flowing back line caused plenty of problems to the home defence.
Even so, the red shirts held firm and the Scarlets had to wait 67 minutes before they reached the home line.
Two O'Gara penalties to one from old rival Stephen Jones were the only points in the first half before that 10 point blitz early in the second.
The Coughlan try coming from a driving line-out moments after Jonathan Edwards had picked up a yellow card.
Rhys Priestland and O'Gara then swapped penalties to create a 13 point gap once again.
But the Scarlets rallied and got a try from close range from replacement hooker Ken Owens that Priestland converted to put the visitors into losing bonus point territory.
Rhys Thomas picked up a second yellow card in the final throes to end any chances of a match winning score.
Now the Scarlets must hope one of the other teams can beat Munster to give them any chance of bridging the gap.
Final Score Munster (6) 19 Scarlets (3) 13
Pens: O'Gara 4
Pens: S Jones, Priestland
Referee: Dave Pearson (England)
Munster: D Hurley; J Murphy, K Earls, L Mafi, S Zebo; R O'Gara, C Murray; W du Preez, D Varley, B Botha, D O'Callaghan, P O'Connell [capt], D Leamy, N Ronan, J Coughlan
Replacements: D Fogarty, M Horan, S Archer, D Ryan, T O'Donnell, T O'Leary, I Keatley, D Barnes
Scarlets: R Priestland; L Williams, S Williams, J Davies, S Lamont; S Jones, G Davies; R Jones, M Rees [capt], R Thomas, L Reed, D Welch, R McCusker, J Edwards, B Morgan
Replacements: K Owens, P John, D Manu, S Timani, K Murphy, T Knoyle, G Maule, V Iongi
With thanks to ERCRugby.