Systems, substitutions & communication – NINE things on Steve Bruce’s Newcastle United agenda
But what went right for the head coach, and what went wrong?
What positives can he take from defeat, and what does he need to change?
Our writer Liam Kennedy takes a look at the NINE key things on Bruce's agenda this week - with a trip to Norwich City next up on the Magpies' calendar.
This always looked like a game which might be won from the bench. And after the first 45 minutes it was certainly playing out the way many expected.
Under-strength Arsenal looked to have as many big guns waiting in the wings as they did on the park - with £72million Nicolas Pepe, former Real Madrid man Dani Ceballos and Alex Lacazette all saved for a (less) rainy day.
United's bench looked stocked, too, though. Maybe not the same levels of quality but Allan Saint-Maximin ready to strike, as well as new boys Jetro Willems and Emil Krafth.
One thing that was missing though, was a midfielder.
Bruce claimed Willems was a midfield option on the bench, but chose to put Matt Ritchie into the middle when Jonjo Shelvey got injured.
The lack of Ki Sung-yeung in the matchday 18, although not injured, maybe came back to bite Bruce on his first competitive weekend in the job.
Longstaff short-term concern
Sean Longstaff has all the tools to be an England international of the future.
The 21-year-old oozes class on the ball, and even looks to have added some bulk to his frame in his time out with injury.
An imposing presence it is no shock that Manchester United were willing to pay £35million to secure his services this summer.
But, and this is a big but, United are reliant on the player to perform, at his best, despite not starting a game since early March.
It's a big ask for a young lad.
Willems went on the field after Shelvey went off and slotted into centre midfield - this caused Bruce to go mental on the sidelines.
It took the players a few minutes to get the message that Bruce wanted - and that was for Willems to go to the left and Ritchie into the middle.
If simple instructions cannot be relayed by players, or understood, that's an issue Bruce needs to stamp out - and sharpish.
Even the slightest bit confusion in a game could prove costly as you get the feeling United are going to need every point they can get between now and the end of the season.
It's fair to say the Paraguayan international didn't really pull up any trees in pre-season.
While his pace is obviously evident, his end product did not really look to be there.
He was absolutely everywhere for United in this one when they were on top.
Bruce needs to find a way of getting the player on the ball as much as possible in areas he can hurt teams.
I am not sure that is as part of a two-man partnership.
Joelinton needs support - but early signs are good
For half an hour the Brazilian was untouchable.
After that he seemed to fade badly.
His touch was still there and his ability to slow the game down - much like Salomon Rondon before him - but the service to him was lacking.
A promising start, and was so close to creating a goal for himself.
A strong, powerful, mobile forward with a lot to offer the Premier League it seems.
Injuries - Shelvey worries
Shelvey has just come off a nightmare season and wanted to hit the ground running this time. Injuty, though, reared its ugly head again, cutting short his decent show against Arsenal.
Lose Shelvey and Ki Sung-yeung can step in, but one more injury and things look very, very light in the centre for United.
Problem is, Bruce can do little to change it.
Picking up where they left off under Rafa Benitez?
United's strong suit under Benitez was their defensive organisation.
To be honest, Arsenal rarely looked like scoring against Newcastle under Bruce - and this has to be seen as a real positive.
Maybe this backline is not trained the same, or drilled in the same manner - Benitez was massive on this aspect of his team's game - but they still stood up to almost everything an albeit under-strength Arsenal had to throw at them.
Positives can be taken from Untied's defensive structure, even though all three will be angry with the goal needlessly conceded.
A system switch on the cards?
Bruce has played 3-5-2 all summer - a slight variation of Benitez's 3-4-2-1.
The latter can be a little more defensive - and it was last season with Ayoze Perez and Almiron tucking in to make it a midfield six, particularly away from home.
The same system could work wonders for United, if tried, with a tweak in personnel.
Allan Saint-Maximin into the team?
Looking at his half hour cameo, Bruce has to look to bring the Frenchman into the reckoning at Carrow Road on Saturday.
A constant desire to make things happen in the final third, combined with pace and direct running - he looks the perfect foil for Almiron and Joelinton beside him.