Arsenal overturned a two-goal deficit but could only earn a point as their Premier League title aspirations were dented at struggling West Brom following their 2-2 draw in Saturday.
Steven Reid put the hosts in front with a header from Chris Brunt's corner.
Robin van Persie nodded against the bar before a horrendous mix-up between Manuel Almunia and Sebastien Squillaci gave Peter Odemwingie a simple finish.
Andrey Arshavin pulled one back with a superb strike before Arsenal equalised through Abdoulaye Meite's own goal.
The Gunners were encamped in West Brom territory late on but could not complete the comeback and were ultimately left to rue Almunia's awful mistake.
The Spaniard was making his first league start since September in the absence of Wojciech Szczesny and Lukasz Fabianski, but there was no excuse for this howler.
See the video below