United were forced to settle for an eighth home draw of the season in another frustrating Old Trafford afternoon.
Despite bossing the ball and dominating territory, the hosts failed to break down Tony Pulis' typically resolute and well organised side.
United have now drawn eleven games in the league - more than any other side - and have dropped 19 points at home.
The Baggies were indebted to former Reds keeper Ben Foster, who made three superb saves to become the latest visiting stopper to turn in an impressive OT display.
Another ex United man, Darren Fletcher, almost won it late on for the visitors when David de Gea palmed his speculative effort on to the bar.
Jesse Lingard flashed a shot wide from distance early on and the returning Anthony Martial then went close with a header at the back post on 18 minutes.
Stand-in skipper Michael Carrick then picked out the man of the match at Middlesbrough, but his dangerous ball in evaded everyone.
Craig Dawson's last-ditch challenge thwarted Martial, Marcus Rashford had a shot blocked and Carrick went close with his follow-up.
United continued to up the ante and almost broke the deadlock with two chances in quick succession on 54 minutes.
Marouane Fellaini was impressive throughout but should done better from 15 yards, and Martial then fizzed a shot wide from distance as the Old Trafford faithful rallied the hosts.
Henrikh Mkhitaryan went close with a clever lob, before Foster had to be at his best to keep out Rashford's stinging effort with a brilliant full-stretch save.
Wayne Rooney was introduced in search of the elusive breakthrough, but it was the visitors who nearly took a shock, and undeserved, lead with 15 minutes remaining.
Fletcher let fly from distance with a shot that de Gea would usually deal with comfortably.
On this occasion however, he fumbled the effort but fortunately for us the ball rebounded back off the bar.
Marcos Rojo headed wide but United continued to press and Foster did well again to deny Rashford.
This time, he tipped wide Rashford's 30-yard free-kick and then saved well with his foot to keep out Rooney late on.
That proved to be the final action of the match as WBA held out for a point to leave United five behind fourth-placed City (albeit with two games in hand).
Overall team performance: 6.5/10
United Faithful man of the match: Marouane Fellaini