A nightmare opening 15 minutes during which they conceded three converted tries without reply sent Harpenden to a second successive home defeat after losing 35-17 to Chiswick.
Although they were the better side for large parts of the remaining 65 minutes, scoring three tries of their own, the damage that had already been inflicted proved too much to overcome.
Harps had begun brightly enough but on five minutes they found themselves 5-0 down after Chiswick full-back Gabs Lowe spotted an absence of defensive cover to touch down in the right-hand corner after chasing his kick ahead.
Worse was to follow three minutes later when Chiswick scrum-half Luca Vannini took full advantage of another glaring gap in the home defence to dart round the blind side of a rolling maul to score in the left-hand corner.
And on the quarter-hour mark wing Tom Steer delivered a further body blow when he rounded off a fine passing move to score a third try for the West Londoners.
Harpenden, to their credit, gradually fought their way back into the game and were justly rewarded with a try before the break by skipper Adam Wheatley after he had peeled away from the back of a scrum to reduce the arrears to 21-5.
However, just minutes into the start of the second half, Steer grabbed his second try after another good kick and chase move.
Harps again refused to buckle and responded with some good rugby. They were duly rewarded on 55 minutes when replacement wing Tristan Francis touched down under the posts following a free-flowing move.
After 77 minutes full-back Jack Haddock pounced on a kick ahead with a try to make the score 28-17.
As Harpenden then went in search of losing bonus-points that had seemed an impossible dream after that awful opening spell, Chiswick centre John Gibson snuffed out their hopes with a fifth try for the visitors in the final play of the game.
Phil Cooper, Harpenden's first-team coach, said: “Although we played a lot better than the previous week, particularly in the second half, we gave ourselves far too much to do. We’ve now got to build on those last 40 minutes as we prepare to face Hampstead this Saturday.”