It was only in stoppage time of this increasingly frenetic tie that Arsenal could truly breathe easily. Alexandre Lacazette, sent on from the bench when authority appeared to be on the wane, leapt to nod a ball over Brentford’s centre-halves before wriggling clear and finishing crisply into a corner. It was a goal to confirm a sixth successive win in all competitions and add gloss to the scoreline, but it said much that the celebrations which followed were tinged with relief.

Brentford, upwardly mobile in the Championship and hugely impressive once they had shed the anxiety which rather inhibited their first-half display, had provided Unai Emery’s team with a real test.

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Alan Judge’s free-kick, swerved over the wall and beyond Bernd Leno, had halved the deficit conceded when they were cowed in the first half, and there were anxious moments for Arsenal to endure in that frantic last half hour as 8,000 Bees fans urged their own on. “They’re a very good team, very organised, tactically very good with their movement,” Emery said. “But this was a match and a result to help us continue to improve.”

The Arsenal manager could take heart from his team’s early dominance, with Danny Welbeck’s double a nudge to the hierarchy that they have a seasoned goalscorer in reserve, albeit one who is out of contract at the end of the season. The England striker, who is yet to make a Premier League start this term, guided a header into the corner from Matteo Guendouzi’s centre early on, the forward having edged away from Romaine Sawyers and Ezri Konsa in a cluttered six-yard box as Brentford’s zonal marking went awry.

His second, eight minutes from the interval, was sidefooted home from Nacho Monreal’s centre with the referee playing advantage after Yohann Barbet’s foul on Stephan Lichtsteiner. Arsenal had swept forward with menace through Henrikh Mikhitaryan, Mohamed Elneny and the overlapping Monreal. “I’m very happy with Danny Welbeck,” offered Emery, before insisting it was up to the club to decide whether he is granted a new contract. Regardless, a simple burst of energy had sufficed to prise apart the visitors.

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Brentford had appeared inhibited, unnerved perhaps facing a side with eight full internationals where, in the recent past, Arsenal would have used a League Cup fourth-round tie as an opportunity to play youth. Emile Smith Rowe, an 18-year-old who had illuminated pre-season, was their nod to homegrown youthful promise, and the older heads around the attacking midfielder appeared to have it settled by the break.

“It took a few words at half-time,” Dean Smith said. “The first goal knocked the stuffing out of us and we never played with the intensity I wanted in the first half. I said to the players we could go and sit behind the ball and let Arsenal win 2-0, or go and ask them a question. That’s what we did, and forced a very good team into mistakes and almost took them to penalties.”

Their rejuvenation would force Arsenal back. Judge’s first goal in 942 days provided some hope, with Sergi Canós firing a presentable chance over the bar almost from the subsequent kick‑off, and there was incision to their approach play and slickness to their passing in what time remained. Yet, desperately at times, Arsenal stood firm until Lacazette, discomforting Konsa and Julian Jeanvier, confirmed progress.