Cotterill, who has attracted considerable interest from Premiership clubs this season, stood out head and shoulders in this game to pave the way for Bristol City's best away win of the season.
Walsall, a pale shadow of the side which played some promising early season football, were outclassed by the South West outfit and the writing appears to be on the wall after only one win in their last 15 games.
The Saddlers, who have failed to score in three of their last four games, have nose-dived into trouble as they have miserably failed to win at home this year.
As a result the Saddlers were extremely disappointing and Bristol City had little trouble collecting three points.
Cotterill, already a Welsh international, quickly appeared as a potential danger as he often put Walsall's defence to panic stations as Ian Roper and Anthony Gerrard struggled against the Robins attack.
Walsall's only bright spot occurred early in the opening 15 minutes when Pablo Mills headed weakly into the arms of Adriano Basso.
With veterans Paul Devlin and Steve Claridge struggling to make an impact, woeful Walsall never appeared likely of carving out a much needed win.
Bristol City turned the game into their favour in the 43rd minute when the impressive Cotterill opened the scoring. Luke Wilkshire created the opening with a low cross which Cotterill calmly guided home with a low shot past Andy Oakes.
The Robins sealed victory in the 51st minute when Roper carelessly brought down Cotterill and substitute Alex Russell converted the penalty.
Mark McCammon should have netted a third goal when he aimlessly blasted his shot over the bar as Bristol City coasted home to a comfortable away win.
Walsall attempted to salvage some lost pride with Michael Leary having a header cleared off the line by Craig Woodman but it was all to no avail in a really dismal performance.
City put the issue beyond doubt two minutes from time when substitute Richard Keogh headed home a Craig Woodman free-kick.