THURROCK, Tilbury, Grays Athletic and Aveley all fell to defeats on Saturday.
Mark Stimson's Fleet suffered a 3-1 defeat at high-flying Leiston.
Matt Blake, who has continued the goalscoring exploits he demonstrated last term, put the home side in front after 28 minutes.
And Leiston doubled their advantage nine minutes later as Jack Ainsley scored from the penalty spot.
But Thurrock halved the deficit just before half-time as Reece Morgan found the back of the net.
However, Fleet were to leave Leiston empty handed, as Blake notched his second of the game six minutes after the break and the visitors were unable to fashion a comeback.
Meanwhile, Tilbury suffered a 6-1 defeat at Bury Town just three weeks after winning at the same venue in the FA Cup.
Bury were awarded a penalty as early as the sixth minute after Ollie Hughes was bundled over in the box by Joe Turpin.
Leon Ottley-Gooch stepped up but put his spot kick high over the top.
But the home side scored three goals in eight first half minutes, thanks to Darren Mills, Ottley-Gooch and Hughes, to give themselves a healthy lead.
Tilbury pulled a goal back on 41 minutes when George Pullen played the ball to Toby Aromolaran, who cut inside to fire home, despite a slight deflection.
Just before the break, the Dockers lost the ball in the middle of the pitch and Camel Ramadan hit a great strike from 30 yards, which flew in to the top corner to restore Bury's three goal cushion at the break.
Ollie Hughes found Ramadan with a dangerous cross just three minutes after the break as Bury continued to be clinical.
On 70 minutes, Tilbury's afternoon got worse when goalkeeper Clarke Bogard saw red for violent conduct and another penalty was awarded.
Turpin took the shirt and saw Ramadan step up and pull his shot wide of the post, to miss the second penalty of the afternoon.
Ramadan did get to complete his hat-trick on 74 minutes though, as found the back of the net after another surge from Hughes.
A rapid attack from Bury on 85 minutes saw Mill hit the back of the net again only to be ruled offside.
Elsewhere, Grays Athletic suffered a 3-1 defeat at newly-promoted Barking.
Jamie Stuart's side went ahead after just five minutes thanks to an own goal.
But Jay Knight got the hosts back on level terms after 18 minutes.
Theo Ola turned the game on its head as he found the back of the net five minutes later, and Dan Gilchrist wrapped up the three points for Barking with a second half effort.
And Aveley were also left licking their wounds as they were seen off by Heybridge Swifts at Parkside.
Swifts, who are flying high in the Isthmian North this term, netted the only goal of the game on 34 minutes thanks to Luke Callander.
And Terry Spillane's side were unable to get back into the game.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here