West Brom missed the chance to reach the Championship summit after Dane Scarlett's stoppage-time header snatched a 1-1 draw for Oxford United.
The Baggies seemed set to move to the top of the second-tier table, at least temporarily after Saturday's early kick-offs, when Karlan Grant drove in a first-half opener at the Kassam Stadium.
Des Buckingham's battling hosts stayed in the clash throughout, however, before Oxford captain Elliott Moore flicked on a long throw-in for Tottenham loanee Scarlett to head into the top corner in the 92nd minute.
Dropping two points late on leaves Carlos Corberan's side fifth in the Championship, with fourth-placed Burnley and league leaders Sunderland yet to play.
Further down the table, Luton Town claimed a much-needed 3-0 win over fierce rivals Watford to ease the mounting pressure on Rob Edwards at Kenilworth Road.
Jordan Clark needed just 11 minutes to open the scoring before Carlton Morris headed home Alfie Doughty's 47th-minute corner to punish some woeful Watford defending.
Substitute Jacob Brown sealed victory in the 91st minute after a long ball from goalkeeper Thomas Kaminski as Luton managed back-to-back league victories over Watford for the first time since 1992.
Luton sit 15th in the table after Saturday's victory, one place and a point behind Preston North End, who fought to a 1-0 win over Coventry City, leaving Mark Robins' side just above the relegation zone.
Emil Riis' 72nd-minute finish proved the difference at Deepdale, where Coventry have never won in 23 league attempts (D8 L15).
Coventry may be looking over their shoulders at Cardiff City, who are level on points with Robins' men after thrashing 10-man Plymouth Argyle 5-0 at home.
Rubin Colwill scored one and assisted two more as Cardiff, under the interim charge of Omer Riza, made the most of Ibrahim Cissoko's first-half dismissal for lashing out at Perry Ng.
Alex Robertson got things going with his 16th-minute opener before the Bluebirds ran riot after the interval with goals from Anwar El Ghazi, Callum Robinson and Chris Willock.
A crushing defeat leaves Wayne Rooney's Plymouth just three points clear of the relegation zone after the Championship's return from the October international break.