Lee Angol saw his penalty saved by Ben Foster after Peterborough's on-loan Martin Samuelsen and experienced West Brom skipper Darren Fletcher had both missed their spot-kicks.

West Brom, just six points above the relegation zone in the Premier League, will go to second-divison Reading in the last 16 of the tournament.

Peterborough had drawn the first meeting at the Hawthorns 2-2 to earn Wednesday's replay and they were ahead after 55 minutes at their compact London Road ground.

Jon Taylor, who had scored in the first game, was on target again with his sixth goal of the season.

But Fletcher, a former Manchester United star, pulled the Baggies level with a smart strike 16 minutes later to send the tie into extra-time.