Ireland internationals Andrew Trimble and Stephen Ferris notched consolation tries but the damage had already been done by a Takudzwa Ngwenya double and scores from Manuel Carizza and Sylvain Marconnet.
The result means Pool Four has been blown wide open with the Ulstermen, Biarritz and Bath locked on one victory each but Humphreys believes his team are still well on track.
"The competition is still wide open," said Humphreys.
"We said at the start of the campaign that we needed to win all our home games, pick up a bonus point win at Aironi and try to get some points at Biarritz and Bath.
"We have four games left and there is plenty to play for.
"We're aspiring to be a top team. We haven't been making the number of errors we did today in previous games.
"This side must keep improving but we've got good players, some top-class internationals who are proven at the highest level.
"There are four big games left but, although we are bruised and battered from this experience, we are not down and out."