The Blues took the lead after Christian Pulisic capitalized on slack defending to make it 1-0.
Chelsea manager, Frank Lampard, has blamed injuries, loss of concentration and for their 2-1 defeat to Arsenal in the FA Cup final on Saturday.
However, the Gunners were level before the break, after Pierre-Emerick Aubameyang levelled from the penalty spot.
Aubameyang netted the winner in the second half, after dribbling past Kurt Zouma to lift the ball over Willy Caballero.
“We had a great start, control of the game but at that point we started getting sloppy and not ramming it home. We got slower in our game, changed the tone of it.”
“Certain circumstances conspired against us in the game,” Lampard told reporters after the game.
On Aubameyang, Lampard said: “He scores two goals, one being a penalty which he earned. We were clear of the threat of long-balls in behind you and that was a frustrating part of the game [as we worked on it].”
Lampard speaking on injuries, added: “Two hamstrings, dislocated shoulder, Willian was injured yesterday, Kante not fit, really. Ruben Loftus-Cheek out.”