Matt Phillips terrorised the Mackems with clinical strikes from Darren Fletcher and Chris Brunt in the first half condemning Sunderland to another defeat.
Moyes's men look helpless and now sit rock bottom of the Premier League, having not won in seven fixtures in all competitions. West Brom, a side with arguably similar resources are now eighth after winning comfortably.
Sunderland produced yet another sorry first half showing as West Brom incrementally broke down David Moyes' Premier League outfit.
The Black Cats were fortunate their midlands opposition took 20 minutes to settle with Brunt and Nacer Chadli both guilty of wasting good opportunities to punish Sunderland.
Ultimately the Baggies grew in confidence as the half wore on, Salomon Rondon saw a strong penalty shout waved away by referee Craig Pawson. The Venezuela international felt Billy Jones man handled him as he rose to head in a hanging Phillips cross.
Several chances followed for Tony Pulis' men, who constantly exposed indecision and nervousness among a team who looked incapable of playing with a three man defence.
Sunderland's next warning came when Phillips inadvertently deflected Rondon's goal-bound header wide. The 25 year old diverted the chance just wide of a beaten Vito Mannone.
Phillips who entered the game in great form continued to brilliantly expose a lack of understanding between Papy Djilobodji and Patrick Van Aanholt on Sunderland's left. He cut inside onto his left and saw low strike parried behind by Mannone.
The inevitable West Brom breakthrough came from the resulting corner, Gareth Mcauley's flick was emphatically volley home by Fletcher on the turn. The ex Manchester United man fired clinically into the corner, but was given infinite time to turn due to Van Aanholt's weak attempts to block the shot.
The second soon followed, Phillips danced through the Sunderland defence, with John O'Shea's attempted challenge being particularly weak. His low drive across goal was pushed away by Mannone straight to Nacer Chadli who inexplicably crashed against the cross bar from point blank range. Chris Brunt clinically dispatched the rebound into the bottom corner, on the half volley.
The second half was largely uneventful with the Baggies happy to sit on a 2-0 lead and Sunderland unable to break them down.
The Wearsiders squandered an early second half chance when Van Aanholt fired into the wall from a free kick just outside the home team's box, he wasted the rebound as well over Ben Foster's goal.
With greater second half possession the Mackems still had no ability to break down Pulis' well drilled defence. A pot shot from Jermain Defoe was deflected wide but wouldn't have beaten Foster anyway.
A glancing Billy Jones header that rolled comfortably towards Foster was arguably the best chance Sunderland's timid attack managed just 20 minutes from time.
Van Aanholt had the England international worried when his effort was deflected and dipping but Foster recovered to tip over.
As time ran out it was West Brom who looked most likely to score getting in behind Sunderland's porous back-line. Substitutes James McClean and Jake Livermore nearly combined for a third, but the Baggies new signing fired high and wide from the Irish international's cutback.
George Honeyman was forced to foul Phillips to end a promising West Brom attack as time petered out.
Worryingly both defeats this week have felt inevitable and routine as Sunderland might finally be falling to relegation.