ARSENAL were dealt yet another blow in the Premier League title race on Sunday.
Despite taking the lead at Stamford Bridge, the Gunners were pegged back and had to settle for a 1-1 draw with Chelsea.
Gabriel Martinelli fired in from a tight angle to break the deadlock on the hour mark.
But ten minutes later, Pedro Neto let fly and squeezed his shot into the bottom corner.
Arsenal squandered big chances to nick all three points - but instead could not fully capitalise on Manchester City's shock defeat at Brighton.
And the draw left both Arsenal and Chelsea on 19 points - nine behind early pace-setters Liverpool.
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But what did we learn about both sides and how did the managers cancel each other out?
SunSport's tactics guru Dean Scoggins revealed all on the latest episode of ...
1. HAS CUCURELLA GOT SAKA'S NUMBER?
Marc Cucurella kept Bukayo Saka very quiet in the Euros final - and he did it again at Stamford Bridge on Sunday because he had a very good plan.
First of all, it's how he attacked him - he went in, he was very physical, he hit him very, very hard.
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But he did it really quickly as Saka received the ball, not after he received it when he likes to touch the ball in field.
Cucurella was already there and that meant Saka was taking the ball where he didn't want to go.
Also, the Spaniard's starting position saw him occupy an inside lane, a narrow position which allowed Saka to have the space on the outside, effectively saying, 'Let's have a race.'
Romeo Lavia, Neto and even Cole Palmer help out defensively to create traffic on the inside, where Saka wants to cut inside on to his left foot.
So it was the early contact from Cucurella and not allowing Saka to spin inside higher up the pitch.
But then when it was deeper, he decided not to engage and challenged Saka to beat him on the outside because he was not giving him the inside channel.
2. COLE HAS GONE COLD
Cole Palmer started the season in red-hot form, scoring seven and assisting five in his first nine games.
However, the last two games have told a very different story with no goal contributions and just one shot on target.
And the explanation comes from Enzo Maresca's box midfield.
The Chelsea gaffer likes to bring Cucurella inside to create a four-man box in the middle - but the left-back was tied up keeping tabs on Saka.
So instead, Maresca instructed Malo Gusto to come inside.
However, the right-back bypassed the holding midfielders and effectively became the right No10, pushing Palmer across to the left No10 - the opposite flank from his devastating inside right position.
Add in the very effective Arsenal defensive triangle of Thomas Partey, Martin Odegaard and Saka stopping Palmer getting the ball and he had another anonymous afternoon.
3. ODEGAARD THE CONDUCTOR
Odegaard is the captain and the conductor - and not just with his attacking intelligence.
It's his pressing, understanding of space and where everyone is around him.
Honestly, he must come off with his arms as tired as his legs because he is constantly waving them, pointing and barking out instructions.
Odegaard is so often the trigger, he is the one who sets the traps.
Kai Havertz did an OK job in his absence. How did they cope without Odegaard?
He is just a sensational player.
And the goal comes from that inside right channel because Odegaard worked it out.
He realised there were four players around him and Saka, so that meant somebody else was free in space and he barely looked before producing that beautiful ball in behind for Martinelli.
If Arsenal are going to go close in the title race, it will be because of Odegaard.
Arsenal ratings v Chelsea
Here's how SunSport's Tony Robertson rated the Gunners:
David Raya - 7
Tipped a shot over the bar early on from Cole Palmer and claimed crosses well. Could do nothing about Neto's crisp strike.
Ben White - 5
Poor when trying to stop a Neto cross that Malo Gusto should have then scored. Booked for a foul on the winger later on.
William Saliba - 6
Steady alongside Gabriel but was more in the covering role so had less to do. Struggled with his line-breaking passes today on the whole. Failed to engage Neto as he raced towards the area before narrowing a shot into the corner.
Gabriel Magalhaes - 6
Made some vital blocks when the midfield was bypassed and was generally the busier of himself and Saliba.
Jurrien Timber - 6
Busy day for the defender in trying to keep Madueke quiet, a task he largely succeeded in. But he wasn't able to heavily influence the game going forward since the ball never really got to him. Most entertaining part of the game before the goal probably came with the 57th-minute throw-in that slipped out of his hands and over his head.
Thomas Partey - 6
Struggled to contain Cole Palmer early on but grew into the game and got on the ball plenty, although he was somewhat wayward with his long-range passing. After a bad touch he managed to poke the ball back to Odegaard before he provided the assist.
Declan Rice - 6
Made some vital defensive contributions to block some Chelsea chances and displayed quick thinking at a free-kick to put Havertz through to score, but was marginally offside. Subbed off after 71 minutes.
Martin Odegaard - 7
Back in the starting XI for the first time since August. Has been a big miss for Arteta's side but may take some time to get back to his best and was on the ball nowhere near enough at the Bridge. Won the ball back before providing the assist for Martinelli's opener.
Bukayo Saka - 5
Showed superb defensive work rate to keep Marc Cucurella in check, though this inversely meant he was unable to contribute as much in attack. Subbed off after pulling up injured in the 79th minute.
Gabriel Martinelli - 8
Should have done better when given the chance to score past Sanchez in the penalty area after Saka won the ball back high. Kept at it and scored against the run of play in the second half with a nice finish to Sanchez's near post. Hooked after 71 minutes.
Kai Havertz - 6
Appeared to have poked home the opening goal with a sharp bit of movement but was fractionally offside. Booked for not going off the pitch when bleeding on his head.
4. CHELSEA'S SANCHEZ FORCEFIELD
Arsenal set pieces have been a major hallmark of their success in recent times but Chelsea defended them better than anyone else has so far this season.
Firstly, they desperately didn't want to give away corners and Robert Sanchez - who made a massive mistake for the goal - was coming out of his area to prevent them.
On the rare free-kicks, the Blues defenders stepped right up to the edge of the box.
But it was at corners where they were particularly impressive as they created a forcefield, a circle around Sanchez to stop the likes of Gabriel and William Saliba a free run at a close-range header.
Nicolas Jackson was the front post as a big man to head clear, the two centre-backs were in front of Sanchez and everyone else was blocking.
Neto even stood with his arms out to block Gabriel from causing more problems.
It was committed defending and highly effective.
Chelsea ratings vs Arsenal
Robert Sanchez - 6
Still punches the ball clear when a catch would be much safer - and reassuring for the fans behind him.
Malo Gusto - 6
Went close with a header in the first-half. But was missing at right-back when Arsenal took the lead through Gabriel Martinelli’s 59th minute goal. The problem with also playing in midfield.
Wesley Fofana - 7
Strong challenges and now fully back from lengthy injury. Also went close to a goal in the second half when he pumped the ball just over.
Levi Colwill - 6
Forging a partnership with Fofana at the heart of defence. Got caught dangerously in possession by Arsenal skipper Martin Odegaard but recovered.
Marc Cucurella - 7
Cracking tussle with Bukayo Saka. Despite being one of only three men on the pitch wearing gloves, including the keepers, Chelsea’s left-back is a formidable defender.
Moises Caicedo - 6
Enjoying a run of form at the moment that includes last weekend’s volleyed equaliser at Manchester United. Strong tackler and smooth through the gears in midfield.
Romeo Lavia - 6
A surprise package keeping £107million Enzo Fernandez out of the team. After a terrible run of injuries is forming some consistency. But any twinge is a scare and came off in the 66th minute.
Noni Madueke - 6
Called up to the latest England squad and is mobile and nippy. Also seemed a bit stroppy and went straight down the tunnel when subbed in the 66th minute. Perhaps needed treatment.
Cole Palmer - 6
Maybe the sore knee is still troubling him. Only trained yesterday for the first time in almost a week. But it hampered his impact on a disjointed London derby.
Pedro Neto - 7
Starting to make his presence felt after being relegated to the Conference League matches. Stunning powerful drive for the equaliser and full of energy.
Nicolas Jackson - 6
Feisty and fiery but went to ground too easily to win a couple of free kicks when he could have done more damage on his feet. Gives everything though.
5. THE ENZO FERNANDEZ INSTINCT
Enzo Fernandez is a top quality footballer - and he has a massive impact on matches.
Maresca likes the defensive pairing of Moises Caicedo and Lavia but Fernandez offers something different and that was evident from the moment he came on.
His introduction was a clever substitution and the right substitution.
He scanned, knew he couldn't go one way and then turned back and the pass for Neto's goal is underrated - the weight was like an invite to move into the area and it was a great goal from the Portuguese winger.
Yes, there were mistakes from Arsenal - Saliba was out of position after going for a wander, Martinelli went to sleep and Neto was given a huge gap.
But do not overlook the quality play from Fernandez.
It gives Maresca a dilemma because Fernandez has such a big impact but doesn't quite fit the system the manager wants to play.
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Is Palmer not producing as much because Fernandez is not playing?
A nice problem to have with a £100million-plus player on the bench.