Manchester United got off to a slow start, with only Nani providing any real penetration or danger as he came close to providing Wayne Rooney and Javier Hernandez with assists as the hosts went looking for the opener. Anderson came the closest in the end, unusually with a headed effort which struck the bar before he blazed over, although he was (wrongly) ruled offside in any case.
West Brom, however, came closest as Stephane Sessegnon, a constant trouble to United's backline with his direct running, broke through the centre and put the arriving Saido Berahino through on goal, albeit from a tight angle, but David de Gea was not to be beaten at his near post and kept the scores level.
David Moyes reacted by withdrawing Shinji Kagawa at half-time, intriguingly replacing him with Adnan Januzaj, but the change was not to be a positive one.
Roman Amalfitano finally broke the deadlock after more poor defending from United, escaping down the right channel with the home side's defence all over the place, his fine solo run eventually taking him one-on-one with De Gea, who he beat with a calm chipped finish.
United weren't kept waiting long for the equaliser, however, with Wayne Rooney's seemingly indirect free-kick eluding everybody in the area and drifting into the far post, out of Boaz Myhill's grasp.
The game became particularly frantic thereafter, with Jonas Olsson and Amalfitano going close to restoring West Brom's lead, the former heading against the bar from a corner before the latter saw a long-range effort clawed away by De Gea. In the end, it was West Brom who scored next, Berahino finding a fine finish to beat De Gea from the edge of the area.
United went looking for an equaliser again, but Marouane Fellaini was correctly ruled offside after he put the ball in the net, while Adnan Januzaj's curling effort was whipped wide of the far post just afterwards. A late siege of the opposition goal failed to materialise, and United were left with a defeat and 12th place in the league.
After some disappointing results in the opening to the season, many people had cited the long upcoming streak of winnable games, The first of those is now out of the way with a defeat, and things ahead could be a lot less predictable than they seem.