Albion 1 Peterborough 1 - verdict
Albion face an unwanted FA Cup replay at Peterborough after red hot striker Craig Mackail-Smith grabbed a late equaliser for the League One side.
The Posh 18-goal hitman forced home Aaron Mclean's right wing cross with four minutes left to delight the 4,000 travelling fans at the Hawthorns.
It was no more than Darren Ferguson's side deserved for a spirited effort against Tony Mowbray's side.
Albion had looked to be heading into the fourth round, after Jonas Olsson headed them in front from a Jonathan Greening corner just after the hour mark.
But they could have been behind at half-time, had goalkeeper Scott Carson not made a couple of fine saves to keep the visitors at bay.
An Albion side shorn of several players by injury looked a little flat before half-time, as the third round tie provided little in the way of goalmouth drama.
Although Albion enjoyed more possession and a few chances before the break, it was the visitors who had the better of the opportunities. Carson twice had to be at his best to keep the home side on level terms.
Midway through the half, the goalkeeper got his fingertips to a half volley from in-form striker Mackail-Smith and pushed it onto the woodwork.
On the half hour he made a fine block low down, to keep out a powerful drive from talented Posh winger George Boyd.
Albion introduced new loan signing Jay Simpson at half-time and duly produced more urgency at the beginning of the second period.
Peterborough keeper Joe Lewis did well to deny Simpson and Baggies captain Jonathan Greening, before the home side finally broke the deadlock.
Olsson stole a yard on his marker to meet Greening's flag-kick at the near post and glance it past Lewis.
But Ferguson's men battled back strongly and in the closing moments Mclean got the better of Marek Cech, with the cross poked home at close range by Mackail-Smith.