West Brom's winless run in the Championship stretched to six games as they blew the chance to open up a four-point lead at the top after a 1-0 defeat at home to Stoke on Monday.
Tyrese Campbell scored the only goal after just nine minutes for the visitors, who moved four points clear of the relegation zone.
A poor run for both the Baggies and Leeds of late has opened up the race for promotion to the Premier League.
West Brom's cushion over third-placed Fulham is down to five points with Brentford and Nottingham Forest just a point further back.
Slaven Bilic's side has now taken just four points from their last 18 available and failed to force Stoke goalkeeper Jack Butland into a serious save.
Campbell, whose father Kevin used to play for West Brom, opened the scoring early on despite Sam Johnstone getting a good hand to the ball.
Stoke then stood firm under an aerial bombardment in the latter stages to continue their upturn in form since Northern Ireland manager Michael O'Neill took charge in November.