A 30-yard strike from Baggies midfielder Graham Dorrans midway through the second half proved decisive.
Rs boss Hughes said: "We can't just wait and think our home form will be enough (to stay up).
"We've talked about it and know we need to improve the away form and pick up points.
"Today was an opportunity for us. We all felt that but what we produced today wasn't good enough.
"Away from home you need to do the fundamentals well and disappoint the home crowd and the team itself.
"Today we gave them too much encouragement and as a consequence they quite enjoyed themselves in the first half."