Well-organised Albion had the game wrapped up with a commanding lead in the first half and piled on agony after the break.
Ironically Chris Brunt, a product of Middlesbrough's prestigious Academy, sent Albion on the road to three precious points with two goals before the interval.
Middlesbrough released the Belfast-born midfield player without him making the first-team grade.
Yet in the match programme, the Northern Ireland international paid tribute to Boro for his grounding.
"I was sorry to leave. You will always feel you have a point to prove, but there is nothing bitter or anything like that.
"I thoroughly enjoyed my time at Middlesbrough and thank them wholeheartedly for everything they have done for me."
Middlesbrough gave a debut to loan signing Sean St Ledger against a side seeking to extend their unbeaten run.
Brunt scored his first goal after 17 minutes with a deflected free-kick into the corner of the net.
His second goal was quite extraordinary and followed a clearance by goalkeeper Danny Coyne as he raced out of the penalty area.
The ball went straight to Brunt and from about 40 yards he fired a volley into an empty net.
West Brom were boosted by this tremendous contribution and Middlesbrough struggled to get back into the game.
In fact, it was men against boys with Albion confirming their superiority with a third goal just before the break from Youssouf Mulumbu.
Mulumbu gave Coyne no chance with a shot from just inside the penalty area.
Middlesbrough needed to stage a remarkable comeback to get anything out of the game but there was not rhythm or threat from the home side.
Adam Johnson, who has been in scintillating form with six goals this season, never even got into the game.
In fact, not one Middlesbrough player impressed against a solid, impressive Albion.
Goals by Roman Bednar and Jerome Thomas in the final ten minutes created wide gaps on the terraces, but sent the 1,153 Albion supporters home happy.