The Gunners were in prime position in fourth place with games in hand weeks ago only to fall into a spell of three defeats away to Crystal Palace, at home to Brighton then at Southampton on Saturday.

Arsenal's old failings - a lack of battling quality, a tendency to choke when the pressure is on - were all revisited in the build-up to this visit to Chelsea, where they started as underdogs with the pressure building.

One win, however significant, does not answer all the questions but this was a night when Arsenal showed they do have hope for development under manager Mikel Arteta - but they must show they can do this again if they are to achieve their goals.

How they needed this and how delighted they will be at the way in which they cashed in on the gifts Chelsea's defence handed them.

Arsenal are still in fifth but they are now only behind Spurs on goal difference with a north London derby to come at Tottenham Hotspur Stadium on 12 May. What an occasion that promises to be.

Arteta's decision to show Pierre-Emerick Aubameyang the door by giving him away to Barcelona in January was coming under understandable scrutiny with Alexandre Lacazette misfiring and no replacement brought in.

He needed to pull something out of the bag and his answer was to relegate the struggling Lacazette to the bench and go with 22-year-old Eddie Nketiah.

Arsenal ended a run of two away games without a goal

Arteta was richly rewarded as Nketiah was in predatory mood, scoring twice, both times taking advantage of horrendous Chelsea defending and fully meriting a standing ovation from Arsenal's fans when he was substituted.

Arsenal now have it in their hands to make the top four but can they gather the belief to make it?

That depends on which Arsenal turns up. If it is the team who shrank in recent games then it is likely they will fall short. If they play like they did here then they will have a great chance.

And in the wider context, Arsenal demonstrated once again that there is the foundation of a very good side here if they can recruit smartly in the summer - with getting the right replacement for Aubameyang key.

Aaron Ramsdale is a developing goalkeeper, Ben White and Gabriel form a good central defensive partnership and in Bukayo Saka and Emile Smith Rowe they have two Premier League gems for now and the future.

These are the cornerstones Arsenal should build on and the reasons why were on show here.

Saka was simply outstanding, especially in a frantic first half when he tormented Chelsea's left flank, setting up Smith Rowe's goal, creating further openings and finally getting the goal he deserved to wrap the win up from the spot in the dying seconds after he was fouled by Cesar Azpilicueta.

This must be the result and performance that kick-starts Arsenal into the decisive phase of the season.

As for Chelsea, this was another miserable night at Stamford Bridge and another example of the defensive frailties that are creeping into their game.

Chelsea should have enough points to ensure they finish third and have the FA Cup final against Liverpool to come but flaws in defence must be a growing concern for Tuchel.

They have now conceded 11 goals in their last three games at Stamford Bridge, four against both Brentford and Arsenal in the league either side of losing 3-1 to Real Madrid in the Champions League quarter-final.

Chelsea, as they were against Brentford, struggled from the first whistle with Antonio Rudiger out injured and Thiago Silva on the bench.

Andreas Christensen is expected to move to Barcelona in the summer and performed like his head was already in Las Ramblas in a dreadful 45 minutes, sending a terrible backpass to Nketiah for Arsenal's opener before he was mercifully removed at half-time.

And then we come to Romelu Lukaku.

Lukaku's £97.5m signing from Inter Milan in the summer was meant to be the final piece of Chelsea's jigsaw after the Champions League win. He increasingly looks like part of another puzzle.

He was laboured, lost too many physical and aerial challenges, snatching at too many chances before he was also substituted. Lukaku has to produce soon but shows no signs.

This was Arsenal's night, the night when belief returned, the night when at least one of the top four contenders woke up to the possibility it is all still up for grabs.