Was not tested by Arsenal's forwards during the entire first half and could do little to keep out Thomas Eisfeld neatly taken opener after the restart. Saved Serge Gnabry's tame penalty in the shoot-out.
Was largely untroubled by Ryo Miyaichi and used his opportunities to venture forward to aid West Brom's attack. Got his side off to the perfect start in the shoot-out with a firm penalty.
Had no problem handling Nicklas Bendtner around the penalty area. Despite this being only his second appearance for West Brom following his arrival in the summer, the 32-year-old was an assured and alert presence at the back.
Defended well against Gnabry, while his dangerous cross in the second half from the left flank should have been met by one of West Brom's forwards.
Allowed Thomas Eisfeld to elude him for the game's opening goal but made up for it by a last-ditch challenge on Bendtner with the Dane clear through on goal. Sliced his penalty well wide of the target.
The Benin international was West Brom's brightest outlet as he tried to conjure chances for his team-mates. His direct dribbles often posed problems for Carl Jenkinson and Arsenal's midfield, while his passing was often accurate. An encouraging display overall.
The central midfielder was on the receiving end of a strong challenge from Isaac Hayden which left him in a heap. Kept West Brom moving but his passing in the attacking third was wayward.
Handled Arsenal's midfield trio alongside Youssuf Mulumbu but was the more assured in possession out of the two.
Had very few opportunities to shine and was, at times, wasteful in possession. Squandered a clear-cut chance at the end of extra-time by slicing a shot wide from eight yards out. A difficult evening for the 24-year-old.
Did not make a significant contribution in the match until the 71st minute when his floated cross was met by Saido Berahino, who headed home West Brom's equaliser.
The 20-year-old, who scored a hat-trick in the last round of the competition against Newport County, looked bright but his end product in the final third looked raw and he squandered possession far too easily. His headed equaliser from Shane Long's cross was well guided though and that was his only clear chance of the match.
Had very little to do in the first half as West Brom's attacks fizzled out when they edged closer to goal. Met Youssuf Mulumbu's rasping drive with a firm save after the break and while he was static for Berahino's equaliser, he was not helped out by his equally statuesque defence.
Surged forward on a number of occasions in the first half in an attempt to get Arsenal's attack moving but his final ball let him down.
The 18-year-old was assured in possession as Arsenal's midfield anchor on his debut but he was lucky to stay on the pitch after a hefty, over-the-ball challenge on Youssuf Mulumbu in the 33rd minute.
The Germany international was largely untroubled at the back in the first half but he should have got closer to Berahino, who was left unmarked and nodded in West Brom's equaliser.
Looked composed alongside Per Mertesacker and restricted West Brom to very few chances to even get on the end of loose crosses.
Dealt with the energetic Berahino with ease but offered little going forward. Scored the penalty which put Arsenal through to the fourth round.
Drifted in and out of the game too easily and really struggled to consistently test Steven Reid.
Had very few touches of the ball in the first half and could not find a way to influence Arsenal's attack as the furthest forward central midfielder. His first clear-cut chance of the game, however, was superbly taken with a low finish past Luke Daniels.
Coped with everything West Brom could muster in their attacking half and looked comfortable in possession.
His return to action did not get off to the best start after he clattered into the post in an attempt to get on the end of Ryo Miyaichi's cross. Had little service in the first half but held up the ball well overall, was tidy in possession and provided a superb through pass to assist Thomas Eisfeld's goal. Dithered on chance in extra-time but scored penalty in the shoot-out.
The 18-year-old looked brighter against Stoke City last Saturday than he did here. Failed to make a significant impact on the right wing and his final ball often let him down. Played a neat ball through to Bendtner in extra-time but the Dane could not take his chance.
Replaced Youssouf Mulumbu to reinforce the midfield and did his job well. His expertly taken penalty put West Brom 3-1 up in the shoot-out after Gnabry's miss.
Came on for Saido Berahino and rattled the crossbar in extra-time with a sharp shot inside Arsenal's box. Missed his penalty.
Replaced Shane Long in extra-time and could have won it for West Brom but his shot was cleared off the line in the closing stages. Struck his side's second penalty straight down the middle and in.
Replaced Mikel Arteta in extra-time as the Spaniard pulled up with cramp.
Came on for Isaac Hayden in the 84th minute for his first-team debut. Calmly tucked away his penalty.
Replaced Thomas Eisfled in the 82nd minute but was unable to make a significant impact. His penalty pulled Arsenal level in the shoot-out.