Arsenal found the Capital One Cup a less hospitable playground than the Premier League and required penalties to advance to a fourth-round meeting with Chelsea. West Bromwich Albion cared little for their status as league leaders and had little difficulty in enforcing a shut-out in extra-time after the match ended 1-1 in normal time.
After falling 3-1 behind in the shoot-out Arsenal appeared doomed only for Albion to miss their final two kicks and hand the visitors a lifeline. Nacho Monreal took it with a thumping left footer into the roof of the net.
With the golden triangle of Mezut Özil, Jack Wilshere and Aaron Ramsey rested, the stage was given over to Bendtner to make some kind of impression a full 25 months after his last Arsenal appearance.
The Dane tried his arm at Sunderland, Birmingham and Juventus on loan and almost joined Crystal Palace in the summer window, yet here he was striving to continue an association that not even Arsène Wenger believes might work.
The manager asked to see some fight from his well-travelled striker. Taking a rather literal view of the appeal Bendtner's first contribution was to clatter into a post. The woodwork won that particular duel leaving Bendtner doubled over on his knees. But the impact seemed to enervate rather than disable the forward, who linked the play resourcefully at the vanguard of an inexperienced Arsenal team showing nine changes from the side that clipped Stoke on Sunday.
West Bromwich do not have the luxury of numbers to play Arsenal's rotation game nor the depth of talent. The victory over Sunderland on Saturday was Albion's first of the season in the league and was sealed by their first league goals at home. They had the first dart at goal when Shane Long headed back a driven cross from Saido Berahino. Long's athleticism surprised Per Mertesacker but not Lukasz Fabianski, who gathered safely.
Thereafter Arsenal settled into marginal dominance with West Bromwich happy to counter through the pace of Berahino and Scott Sinclair, who probed in the first half the part of the pitch that staged Paulo Di Canio's last stand.
Arsenal fashioned a series of raids down the right towards the end of the half with Serge Gnabry and Isaac Hayden prominent, but it was Albion who went closest with the only shot on target in the first 45 minutes, a rasping free-kick from Steven Reid, tipped over by the flying Fabianski.
Arsenal added a degree of urgency at the start of the second half to the control of the first and for 10 minutes camped in the West Brom half. There was still too little to do for West Brom keeper Luke Daniels, who would have needed a crane to gather Thomas Eisfeld's errant strike from 20 yards.
The main threat to Arsenal was complacency, as demonstrated by the poor pass of Mikel Arteta that set Stéphane Sessègnon free. The Benin international bound into the inviting acres behind the stranded Arteta only to overrun the ball as he approached the box.
Suitably chastened Arsenal responded with an incisive raid at the other end, Bendtner playing his part, neatly threading the ball through for Eisfeld to wrong foot Daniels and plant the ball briskly in the net.
Bendtner's contribution triggered a flow of love from the terrace behind the goal occupied by Arsenal fans, who dug deep into their song book to chorus his name. "Super Nicklas Bendtner" indeed. West Brom had half an hour to engineer a response. It took them all of 10 minutes, Berahino heading home at the far post after Long lifted the ball back across goal.
This was just what the contest needed, the final 20 minutes fought out in the more traditional cup-tie manner. West Brom piled forward and with greater poise in front of goal Berahino might have sealed victory in normal time. Played in again by Long the Burundian flyer advanced down the right only to plant his shot high over the bar.
In added time Carl Jenkinson whipped in a dangerous cross from the right that evaded both Bendtner and Eisfeld sliding in at the far post. It proved the last opportunity. Extra time beckoned.
Man of the match Berahino.
Match rating 7/10.
Referee R Madley (West Yorkshire).