ALBION suffered penalty shoot-out heartbreak to exit the Capital One Cup at the third-round stage.
Craig Dawson and sub Morgan Amalftano both failed to hit the target with their spot-kicks which paved the way for Nacho Monreal to wrap up a 4-3 success.
Albion were the better team in normal time but fell behind on 61 when they were punished for conceding possession inside their own half by Thomas Eisfeld’s cool finish.
However, the Gunners’ lead lasted just 11 minutes, with Saido Berahino deservedly heading the hosts level from a Shane Long centre – his fourth goal in the competition.
Both teams had chances to nick it during a thrilling period of extra-time, with Amalfitano going closest by smashing the bar in the 116th minute.
Arsenal will host London rivals Chelsea in the next round.
The teams squared up tonight for the fourth time in the competition inside a decade.
Long returned from a two-game injury absence in attack while skipper-for-the-night Steven Reid made his first appearance of the term following a pre-season calf problem as Clarke rang eight changes.
Dawson, Diego Lugano, Goran Popov, Luke Daniels, Graham Dorrans and Berahino also earned recalls.
Arsene Wenger went one step further than his opposite number by making nine changes, which included a return for Mikel Arteta from injury.
Albion threatened first when Reid whipped over a terrific cross from the right, which Long headed back across goal. The ball ricocheted goalwards off Carl Jenkinson but into Lukasz Fabianski’s arms.
Arsenal broke with purpose down the left in the eighth minute but Ryo Miyaichi’s centre flew just over Nicklas Bendtner’s head and Daniels gathered.
There was a competitive edge to this clash but chances remained at a premium as the game reached the 20-minute mark.
The first real shot of the game did not arrive until the 23rd minute, when Dorrans hacked wildly wide from just inside the box.
Dorrans went a little closer two minutes later when his 25-yard free-kick clipped the Arsenal wall and flew out for a corner. From Dorrans’ ensuing flag-kick, Dawson won the aerial battle and saw his looping header tipped over by Fabianski.
Dorrans had certainly got a taste for shooting at goal but his next effort, from an angled 20-yard free-kick, failed to trouble Fabianski.
Arsenal didn’t threaten again until the 40th minute, when Monreal’s shot was blocked in the box by Dawson.
Three minutes later, Albion had a moment of concern when Daniels lost his footing as he went for a Serge Gnabry corner. Thankfully, the ball fell kindly for Albion and Dawson cleared.
Albion continued to look the more threatening of the two sides, though, and Fabianski was called into action in first-half stoppage time when he leapt high to his right to tip over Reid’s dipping 35-yard set-piece.
The Gunners were the first to go close after the break when Jenkinson surged across the edge of the box to tee up Eisfeld, who curled harmlessly over from 20 yards.
Albion began to build up a head of steam at the other end by winning a couple of corners – but they came to naught.
The Baggies were on top, though, and after Stephane Sessegnon’s surging right-wing run, Youssouf Mulumbu saw a fierce 20-yard volley brilliantly tipped over by Fabianski.
However, Albion’s hard work unraveled in the 61st minute. After Mulumbu conceded possession deep inside the hosts’ half, Bendtner slipped in Eisfeld who gave Daniels no chance with a cool 15-yard finish.
The Baggies regrouped but Popov shot wide of the near post from 20 yards.
Back came Arsenal and Lugano had to produce a vital block to prevent Gnabry’s 15-yard drive troubling Daniels.
But normal service soon resumed, with Albion pegging the visitors deep in their own half. And they converted a sustained spell of pressure into a 72nd-minute leveller. After Dorrans’ corner had been flicked across goal by Dawson, Long hooked the ball into the six-yard box and Berahino powered a header past Fabianski.
Albion now pressed for a winner and Scott Sinclair had a 20-yard shot deflected wide for a corner. On 82, a flowing move led to Berahino firing over from 18 yards.
It wasn’t until seven minutes from time that Arsenal recorded their next shot at goal, with Gnabry dragging his effort wide of the far post from Bendtner’s header.
There was one final scare for Albion in the second minute of stoppage time, when Jenkinson’s superb right-wing cross just evaded Gnabry at the back stick. Referee Robert Madley then blew up for extra-time.
Clarke rang two changes during the short interval, replacing Mulumbu and Long with James Morrison and Markus Rosenberg.
Albion again pushed Arsenal back from the restart, but it was Arsenal who went close first. On 94, Daniels needed two attempts to snaffle Miyaichi’s deflected shot.
The Baggies got caught on the counter-attack three minutes later, with Gnabry putting Bendtner clean through. The Dane had only Daniels to beat but he didn’t even get a shot away after being dispossessed by Dawson’s brilliant last-ditch tackle.
Arsenal went close again just before the interval when sub Chuba Akpom drilled just wide of the far post from a tight angle.
Five minutes after the restart, Fabianski had to produce a fine near-post save to keep out Rosenberg’s volley from Popov’s centre.
Back came Arsenal and Daniels showed a safe pair of hands from sub Hector Bellerin’s 20-yard grass-cutter. Bellerin was at it again moments later, shooting just wide from the edge of the box.
But there was real Albion agony in the 116th minute when sub Amalfitano spun superbly in the box and smashed the bar with a 15-yard drive.
And Rosenberg went just as close 60 seconds later when he raced onto Amalfitano’s pass, dinked the ball over Fabianski and shot goalwards, only to see his effort blocked on the line by Thomas Vermaelen.
In the 118th minute, Sinclair volleyed Albion’s last chance just wide from Rosenberg’s centre – before the tie went to penalties.
Albion got their noses in front in the shootout when Daniels kept out Gnabry’s spot-kick.
But Dawson and Amalfitano both sent their penalties wide, paving the way for Monreal to wrap up a 4-3 shootout win by sending Daniels the wrong way.
1-1 Reid – scored; Bendtner – scored.
2-1 Rosenberg – scored; Gnabry – saved.
3-2 Morrison – scored; K Olsson – scored.
3-3 Dawson – missed. Akpom – scored.
3-4 Amalfitano –missed. Monreal – scored.
ALBION (4-4-1-1): L Daniels; Reid (c), Dawson, Lugano, Popov; Berahino (Amalfitano 101), Mulumbu (Morrison 91), Dorrans, Sinclair; Sessegnon; Long (Rosenberg 91). Subs not used: Camp (gk), McAuley, J Olsson, Jones.
ARSENAL (4-2-3-1): Fabianski; Jenkinson, Mertesacker, Vermaelen (c), Monreal; Arteta (Bellerin 95), Hayden (K Olsson 84); Eisfeld (Akpom 82), Gnabry, Miyaichi; Bendtner. Subs not used: Viviano (gk), Flamini, Park, Iwobi.
GOALS: ALBION – Berahino (72). ARSENAL – Eisfeld (61).
BOOKINGS: ALBION – Lugano (foul 88), Popov (foul 90), Reid (foul 99). ARSENAL – Hayden (foul 33), Monreal (foul 36), Vermaelen (foul 52), Arteta (foul 85).
REFEREE: R Madley (West Yorkshire).
ALBION STARMAN: Craig Dawson.