Essex beat Surrey by four wickets with just a ball to spare at Chelmsford to go joint top with Kent at the head of the Twenty20 Cup South Division.
Scott Newman batted through for an unbeaten 81 in 60 balls as previous leaders Surrey amassed 165-5.
But, after Alastair Cook's 35, his England team-mate Ravi Bopara was crucially dropped on his way to 53.
And, despite two wickets going down in the final over, Grant Flower kept his nerve to seal victory on 169-6.
Surrey are in action again on Monday at the Rose Bowl against Hampshire (1730 BST).
But Essex have until Monday night (1 June, 1730 BST) to wait for their next game, when they meet also unbeaten Kent at Chelmsford.
And, following the two sides' rained-off opener at Canterbury last Monday night, this game, even at this early stage, could be the group decider.