SO much for Steve Bruce’s January signings transforming Newcastle United’s fortunes then. All three of the Magpies’ recent additions started at the Emirates Stadium, but they were unable to prevent their side suffering their heaviest defeat since September as they completely collapsed in the second half. Level at the interval, Bruce’s players were a shambles in the second 45 minutes.

The fact that two of Arsenal’s goals came in stoppage time might have given the scoreline a slightly lop-sided feel, but the timing of the strikes should not temper the sense of alarm that accompanies Newcastle’s latest capitulation.

The Magpies remain seven points clear of the relegation zone, but they are not safe yet. Play like this in their next three matches against Crystal Palace, Burnley and Southampton, and they will head into the final two months of the season in deep trouble.

The most alarming aspect of today’s collapse is that, for half of the game, it did not look like coming. Newcastle were arguably the better team during an even opening period, counter-attacking effectively, creating chances for Sean Longstaff and Joelinton, and successfully shackling an Arsenal team that looked a pale imitation of some of the great Gunners side that have thrashed the Magpies at the Emirates in the past.

Yet from the minute the whistle blew at the start of the second half, the visitors were a completely different proposition. Defending on the edge of their own 18-yard box, they invited the kind of pressure Arsenal had been incapable of creating before the break.

Mistakes started appearing, and having attacked impressively during the first half of his full Newcastle debut, Valentino Lazaro’s defensive limitations were alarmingly apparent as the Gunners effectively settled things with two goals in the space of three minutes shortly before the hour mark.

Lazaro, a January loan signing from Inter Milan, was at fault for both goals, losing Pierre-Emerick Aubameyang as he headed home Pepe’s cross before he was beaten far too easily as Bukayo Sako set up a second goal for Pepe.

Suddenly, Newcastle were all at sea, and while Allan Saint-Maximin almost pulled a goal back with a solo strike that crashed against the post, Arsenal had chances of their own to extend their lead.

Aubameyang also hit the woodwork before late goals from Mezut Ozil, who profited from a rare goalkeeping howler from Martin Dubravka, and Alexandre Lacazette, who scored despite only coming off the bench in the 84th minute, embellished Arsenal’s win.

Newcastle’s implosion was reminiscent of so many of their previous embarrassments on this ground, and was especially troubling given how much stock Bruce and his players have put in being resilient and well-organised this season. If they don’t have those attributes to fall back on anymore, what else have they got to offer?

Certainly not an effective attacking threat, with yesterday’s failure to find the net meaning they have been unable to score in nine of their 26 league games this season. Clearly, that is a wretched record, but Bruce will once again point to a lack of alternative options as an explanation for why Joelinton led the line for the full 90 minutes despite being predictably ineffective throughout. Without a striker on the bench, Bruce was unable to change anything. As a result, his decision to sign the injury-prone Andy Carroll looks less and less astute with every week that passes.

Saint-Maximin had his moments, most notably when he drilled his second-half strike against the upright, but he cannot be expected to carry Newcastle’s attacking burden by himself. There were periods in the first half, when Lazaro overlapped down the right and Miguel Almiron busied himself in an attacking-midfield role, when the visitors threatened to cause the Arsenal defence problems. In reality, though, they were few and far between.

Newcastle’s best two chances of the game came in a 60-second spell in the first half. The first came from a corner, with Arsenal’s determination to mark Newcastle’s central defenders in the 18-yard box meaning Sean Longstaff was left all alone 25 yards out. Lazaro floated the ball into his path, and while Longstaff didn’t quite connect with his first-time effort, a hefty deflection off Dani Ceballos would have taken the ball in had Bernd Leno not made a good scrambling save to his left.

Sixty seconds later, and Saint-Maximin was dribbling his way into the left-hand side of the area before squaring the ball towards Joelinton. Unfortunately, his pass was marginally behind the Brazilian, who could only prod a stretched effort wide of the target.

Arsenal’s initial ineffectiveness meant they were the best two chances of the opening period, with the hosts’ only first-half moment of note coming to nothing when Joelinton cleared Shkodran Mustafi’s hooked effort after Dubravka had failed to clear with an attempted punch.

At that stage, Arsenal looked every bit as limited as their opponents, but the game turned decisively during a three-minute spell at the start of the second half.

Aubameyang had been relatively quiet during the opening 50 minutes, but he only had to make one run to change the course of the match. Drifting between Lazaro and Federico Fernandez, he was left with the simple task of nodding home Pepe’s chipped cross from eight yards out.

Three minutes later, and Newcastle’s defence was found wanting once again. Lazaro was undone close to the touchline, with Sako slipping the ball between his legs before delivering a low cross into the box. Pepe took advantage, slotting home a first-time finish as the visitors’ marking disappeared.

Aubameyang almost added a third with a chipped effort that sailed over Dubravka before landing on the top of the crossbar, and while Ciaran Clark wasted a good opportunity to haul Newcastle back into the game as he dallied over his shot in the area, enabling David Luiz to stick out a leg to block, Arsenal’s second-half dominance was pronounced.

It was emphasised by the two goals they scored in stoppage time as Newcastle’s defensive discipline was nowhere to be seen.

Ozil scored the first, although the German’s goal owed much to a rare aberration from Dubravka, who bundled the ball into his own net after it was fired straight at him from close range.

Lacazette squared the ball into Ozil’s path, and the substitute claimed a goal of his own a couple of minutes later. Pepe, whose second-half performance was a key factor in Arsenal’s transformation, pulled the ball back, and Lacazette found the corner of the net from eight yards.