Newcastle United suffered a 4-0 defeat against Arsenal following a second-half capitulation at the Emirates.

The Magpies more than held their own in the first half but a quick fire double from Pierre-Emerick Aubameyang and Nicolas Pepe left the visitors with a mountain to climb before the hour mark.

Although Ciaran Clark and Allan Saint-Maximin both had good opportunities to get Newcastle back into the game, the Gunners went on to run riot in the final minutes and goals from Mesut Ozil and Alexandre Lacazette made it a humiliating defeat.

Here are five things we learned from the game.

Just what happened after half-time?

Newcastle produced one of their best first-half performances in recent weeks at the Emirates - looking threatening on the counter-attack and defending manfully - but the Magpies made a sloppy start to the second half, which cost them dearly.

Newcastle may not have won at the Emirates since 2010 but this was not an Arsenal team to be feared. The Gunners are unbeaten in 2020 but, going into this game, Mikel Arteta's side had not won in the Premier League since New Year's Day and had won two fewer league games than Newcastle.

Naming an attack-minded line-up, you sense Bruce felt the Magpies could get something from this fixture but the game quickly ran away from the visitors in the second half, which brought back memories of the collapse at Leicester in September.

Sloppy defending costs Newcastle dearly again

As has so often been the case this winter, sloppy defending has cost Newcastle dearly in defeat. The Magpies, who put that humiliating defeat at Leicester behind them with a series of solid displays, have given away a number of poor goals in recent weeks and shot themselves in the foot time and time again in the second half at the Emirates.

The defending for Pierre-Emerick Aubameyang's opener left a lot to be desired as he rose highest to meet Nicolas Pepe's cross; Valentino Lazaro was embarrassed by Bukayo Saka for the second; Martin Dubravka fumbled Mesut Ozil's third; and Newcastle players looked like they were waiting to be put out of their misery when Alexandre Lacazette's scored Arsenal's fourth.

After Arsenal scored two goals in three minutes before the hour mark, Newcastle stemmed the tide - Ciaran Clark even had a golden opportunity to pull a goal back - but the floodgates opened again at the death as the Gunners scored two goals in the final few minutes.

There's a reason why Newcastle play with a back three

Steve Bruce regretted his decision to shift to a back four against Leicester in September and while the Newcastle head coach wants his side to evolve, he has repeatedly stressed they are not yet ready to play with four at the back.

But, in an effort to get back into this game, Bruce threw on Isaac Hayden and Matt Ritchie with 20 minutes to go and switched to a 4-1-4-1.

While Allan Saint-Maximin hit the post just a couple of minutes later, a leggy Newcastle became too open as the game wore and Arsenal took full advantage, turning a 2-0 win into a 4-0 humiliation.

Perhaps, it would be a surprise if Bruce moves away from a back five again this season.

Ciaran Clark's injury is a big worry

Newcastle had already conceded two goals before Ciaran Clark went off with a nasty-looking injury on 83 minutes, following a heavy collision with Saka, but it got even uglier after the Ireland international was substituted.

Bruce has had Florian Lejeune and Fabian Schar available in recent weeks but there has been a reason why he has stuck with Ciaran Clark since his first league start of the season back in October.

The underrated 30-year-old has been a solid performer and been at the heart of the Magpies' most impressive defensive performances this season so if he is to have a spell on the sidelines, that will be a blow for Newcastle - even with the options in reserve.

A baptism of fire for Danny Rose and Valentino Lazaro

Steve Bruce made six changes from the side that beat Oxford United last time out and handed full debuts to Danny Rose and Valentino Lazaro.

The Newcastle head coach had previously 'aired on the side of caution' when it came to starting his new arrivals 'in case they weren't physically right' but, following the winter break, felt they were both ready to start.

Valentino Lazaro of Newcastle United and Pierre-Emerick Aubameyang of Arsenal during the Premier League match between Arsenal FC and Newcastle United
Valentino Lazaro of Newcastle United and Pierre-Emerick Aubameyang of Arsenal during the Premier League match between Arsenal FC and Newcastle United

One of the main reasons Rose and Lazaro joined Newcastle was to get get some game time ahead of Euro 2020  and while there were positives to take from their first-half performances, they naturally tired as the game wore on.

Lazaro and Rose know they will have to get up to speed quickly to really nail down a starting place. The same goes for fellow new arrival Nabil Bentaleb.