London Welsh secured a losing bonus point to leave the teams locked at the top of Pool C.
Having raced into a 16-0 lead after 20 minutes with a try from scrum-half Paul Marshall and three penalties and a conversion from out-half, Niall O’Connor, the Ravens switched off and by the interval there were just five points in it.
Full back, Ed Lewis-Pratt and Gordon Ross each kicked a penalty and centre Neil Starling went over for a try.
Ravens made a storming start to the second half with a magical try from Timoci Nagusa, but the English Championship side came back again, only for the Ravens to hold out.
RAVENS: M McCrea; T Seymour, M Allen, I Whitten, T Nagusa; N O’Connor, P Marshall; B Young, N Brady (capt), T Court, N McComb, R Caldwell, T Anderson, W Faloon, R Diack.
Replacements: A Whitten for Court (70), E O’Donoghue for Diack (68), C Willis for Marshall (70), D Cave for Nagusa (52).
LONDON WELSH: E Lewis-Pratt; P Sampson, N Starling, S Whatling, E Classens; G Ross, B Stevenson; D Williams, G O’Meara, M Holford, M Corker, M Powell, J Mills (capt), M Hills, T Brown.
Replacements: N Bonner-Evans for Mills (52), R Lewis for Stevenson (68), P Mackey for Whatling ( 51).
Referee: Leo Colgan (IRFU)