Its lead over nearest rivals Leeds United remains at two points, however, after Marcelo Bielsa's side was held to a 1-1 draw at Preston North End.
Basement club Barnsley looked set for a precious win at the Hawthorns after Cauley Woodrow put them two goals ahead after 24 minutes.
Slaven Bilic's side turned things around in the second period, though, with an own goal from Bambo Diaby reducing the deficit in the 68th minute. They ensured a point with nine minutes remaining thanks to Matheus Pereira's third league goal of the season.
Leeds missed the chance to leapfrog the Baggies at the summit as it was held by fellow promotion chaser Preston at Deepdale.
Tom Barkhuizen fired home from close range in the 74th minute to give Alex Neil's side hope of jumping above Leeds into the automatic promotion places.
But on-loan Arsenal striker Eddie Nketiah had other ideas, coming off the bench to head home a leveller three minutes from time.
Sheffield Wednesday moved up to third after a narrow 1-0 win over Stoke City, while Brentford and Birmingham City was victorious against Swansea City and Blackburn Rovers respectively.
Elsewhere, new Millwall boss Gary Rowett was watching on as the Lions drew 2-2 with Cardiff City - the same result as the clash between Queen's Park Rangers and Reading.
Brentford was in ruthless form against Swansea, sealing a 3-0 win at the Liberty Stadium.
Said Benrahma claimed his first goal of the campaign to give the visitors the lead before Jake Bidwell's own goal doubled its advantage.
Any hopes the home team had of clawing their way back into the game were extinguished early in the second half when Bryan Mbeumo added a third.
Elsewhere, Maxime Colin's first-half goal secured a 1-0 victory for Birmingham, while Tom Bradshaw cancelled out goals from Danny Ward and Junior Hoilett to seal a point for Millwall against Cardiff.