Middlesex 161 (Williamson 53, Amir 3-19) beat Essex 160 for 6 (Walter 30, Gohar 2-20) by one run
Tom Helm held his nerve in a nail-biting final over as Middlesex began the post Richard Johnson era with a one-run victory over Essex, three years to the day after their last Vitality Blast win at Lord's.
Forty-eight hours on from Johnson being relieved of duty, Helm (2 for 31) claimed the crucial wicket of Luc Benkenstein in defending 10 off the final six balls to see Middlesex home.
Essex had appeared to be cruising at 106 for 2 thanks to a stand of 54 between Paul Walter and Jordan Cox, but Zafar Gohar's 2 for 20 put the brakes on the chase, leading to the breathless finish.
Middlesex earlier collapsed from 108 for 1 to 161 all out, failing to build on
Kane Williamson's 53 in 31 balls, the former New Zealand Test captain's first half-century for the Seaxes. Simon Harmer (2 for 34) and Benkenstein (2 for 26) started the slide with Mohammed Amir polishing off the tail.
Middlesex came out swinging at the start of the new era, but rather than aggressive, much of the batting was frenetic.
Williamson swung one from Shane Snater over the short boundary, but among his other early fours was a top edge over wicketkeeper Cox's head.
Stephen Eskinazi, save for successive sweeps to the square boundary struggled to find the middle of the blade before being brilliantly caught down the leg-side by Cox.
Williamson steadily found his groove, a glorious straight six helping him to 50, but once he departed to the next delivery caught at long-leg off Noah Thain the collapse was on.
Ben Geddes was dropped off both his first two balls and lasted five in total before lifting Benkenstein to deep midwicket and Max Holden's somewhat skittish effort was ended by Harmer as the Essex spinners ripped through the heart of the middle-order.
Essex openers Dean Elgar and Michael Pepper came out in a big hurry to get the chase done, the latter planting successive deliveries from Naavya Sharma over the ropes. Elgar in his turned cracked a four to the fence at point as they rattled up a 50-stand in 27 balls.
Pepper chipped Gohar to mid-off soon afterwards and Elgar sent the first ball of Helm's next over to short third.
Walter though clubbed Helm into the stands and expertly paddled the spin of Luke Hollman to fine leg for four, while Cox cut powerfully square of the wicket and through cover as another 50 partnership came in 35 balls. Again, both fell in quick succession, Walter undone by a Sharma bouncer while Gohar castled Cox.
The hosts thought they had Benkenstein caught by Helm off Hollman, but after conferring the umpires ruled not out. Nevertheless, Matt Critchley holed out off Noah Cornwell as the tension mounted.
Charlie Allison thick-edged and ramped Ryan Higgins for four leaving 10 needed from the last. Benkenstein went for glory but holed out to Geddes in the deep, and while two twos were scrambled four was needed off the final delivery. Thain clothed it to deep mid-off, where Geddes collected and returned to spark celebrations from the hosts.