Emile Smith Rowe has now scored in back-to-back Premier League games for Arsenal
Chelsea boss Thomas Tuchel says he takes full responsibility for his side's home defeat by Arsenal after making seven changes for the game.
The Blues had claimed an impressive win at Manchester City on Saturday to delay the Premier League champions' title celebrations and boost their hopes of a top-four finish.
However, with an FA Cup final against Leicester coming up on Saturday, only four players retained their places in Tuchel's side for Wednesday's visit of Arsenal.
It was still a strong line-up but a mistake by Jorginho in the first half allowed Emile Smith Rowe to score what proved to be the winning goal for Arsenal and, although Chelsea dominated possession and hit the woodwork twice late on, they couldn't find an equaliser.
Chelsea remain fourth on 64 points but the defeat will give their rivals hope of sneaking into the top four. They are six points ahead of West Ham, who have a game in hand, and seven ahead of Liverpool, who have two games in hand on the Blues.
"I'm a bit angry that we had so many changes, that's on me," said Tuchel.
"I'm not so happy in the end with the line-up, but I didn't know what would happen, I didn't feel us today like I normally do and we can't expect to win games if we're not 100% in games.
"I'm not happy with what I saw, I have my responsibility because I picked the line-up, but the performance was the performance."
Jorginho's error will have been disappointing for Tuchel. The midfielder misjudged a pass back that was in danger of trickling over the line before Kepa Arrizabalaga managed to claw the ball away but only to Pierre-Emerick Aubameyang, who teed up Smith Rowe to slot in.
Christian Pulisic thought he had equalised on the hour but his strike was ruled out by the video assistant referee for offside, while Bernd Leno pushed Kurt Zouma's header onto the bar in injury time before Olivier Giroud's volley also bounced back off the woodwork.
The victory also meant the Gunners completed the double over the Blues for the first time in 17 years to boost their own hopes of ensuring they are playing European football next season.
Arsenal are eighth and just one point behind Tottenham in seventh, although have played a game more.
Off day for Chelsea gives hope to chasing pack
Christian Pulisic had a goal ruled out by VAR for offside for Chelsea
Chelsea have been hugely impressive under Tuchel and, while the immediate goal is getting the points required to cement a top-four finish this season, the signs are good that they should be title challengers next term.
The two-legged win against Real Madrid in the semi-final of the Champions League highlighted how difficult a side they are to beat but this game also showed that they can sometimes be their own worst enemy.
Jorginho's mistakes, when he attempted a blind pass back to Kepa, was the eighth time the Blues have made errors leading to opposition goals in the Premier League this season, a number surpassed only by Liverpool (nine) and Chelsea's most in a single league campaign since 2015-16.
Despite that Chelsea had plenty of opportunities to get a result but were wasteful in front of goal. Kai Havertz should have scored before Smith Rowe's opener but blazed over when one-on-one while Giroud also had a good chance to equalise in the second half.
Chelsea may have had half a mind on Saturday's FA Cup final against Leicester and they are still in a great position to finish in the top four but the defeat - only their third under Tuchel - will give hope to the chasing pack.
Liverpool's next two games are away to Manchester United and relegated West Brom and if they are to win those they would only be a point behind Chelsea with two games remaining.
"We didn't have a shot for almost the whole second half," added Tuchel.
"Maybe we deserved this, we will learn something."
A welcome win, but still work to do for Arsenal
A win at a strong Chelsea side is certainly a very good result and one that keeps alive Arsenal's hopes of avoiding missing out on European football for the first time in 27 seasons.
The performance was for large periods a disappointing one as, bar Smith Rowe's tap-in following Jorginho's mistake, they struggled to create anything of note as they spent the majority of the game camped in their own half.
But to their credit they were organised in defence, particularly when they came under pressure late on and while they rode their luck at times it was another positive result as the Gunners try to put behind them the disappointment of failing to reach the Europa League final.
Arsenal still look a long way off a side that will challenge for the top four again anytime soon but it is now three Premier League wins in a row and, with games against Crystal Palace and Brighton remaining, they have the opportunity to finish an underwhelming season in a positive fashion.
Arsenal boss Mikel Arteta said: "I am really happy with a lot of things we have done, right from the first minute, the attitude and the desire to win that we showed.
"We had to dig in - you have to against this team because they are a fantastic team. We did it and we put [in] everything that we had to try to get the best possible result, and we did it."
-- Courtesy of BBC Sport