Bishop's Stortford suffered their first defeat since January 8 and conceded for the first time in 1,088 minutes away to the Ambers on Easter Monday
Bishop's Stortford kept a 12th consecutive clean sheet and are unbeaten in 17 matches following 3-0 home win over Potters Bar Town.
Blues' 3-0 win over Folkestone is fifth victory on the bounce, extends unbeaten run to 15 matches and brings 10th successive clean sheet.
Two goals in less than a minute earned Bishop's Stortford a 2-0 win at Wingate & Finchley in the Isthmian League, Premier Division on Saturday
Bishop's Stortford were held to a second consecutive 0-0 draw at home to Horsham on Saturday as they fell two more points adrift of leaders Worthing
Ryan Charles scores the first and earns penalty for the second in 2-0 win that leaves Blues unbeaten in seven and only one defeat in 22 in league.
Stortford, who had majority of possession and chances at Leatherhead, still climb to third in Isthmian League Premier Division.
Fourth-placed Bishop's Stortford make it nine goals in two games and have now lost only once in their last 17 league games.
Jimmy Wallace opened his Bishop's Stortford account as they thrashed Brightlingsea Regent 5-0 in the Isthmian League, Premier Division on Saturday
Bishop's Stortford suffered their first defeat in 90 minutes for 19 games as they went down 2-0 at Hornchurch on Saturday
Anthony Church scored his second goal of the season as Bishop's Stortford claimed a 1-0 victory at Cray Wanderers in the Isthmian Premier on Saturday
Bishop's Stortford picked up their first clean sheet in eight games and moved up to fifth with a 0-0 draw at Folkestone Invicta on Tuesday night
Johnville Renee's goal was only worth a point as Bishop's Stortford drew 1-1 at home to Carshalton Athletic in the Isthmian Premier on Saturday
Bishop's Stortford were denied a fifth consecutive win as they drew 2-2 at Merstham in the Isthmian League, Premier Division on Tuesday night
Goals from Merrifield (2), Foxley, Harris and Charles against Leiston set up Blues for possible tie with National League side in last 64.
Foxley free kick followed by Merrifield brace within three minutes of coming off the bench in Stortford's sixth successive home game.
Johnville Renee came off the bench to score an injury-time winner as Bishop's Stortford beat second-placed Enfield Town 2-1 on Tuesday night
Bishop's Stortford progressed to the second round of the Buildbase FA Trophy with a 2-1 home win over Chipstead on Saturday
Bishop's Stortford were denied maximum points late on at home as a Lewes equaliser ensured their Isthmian Premier meeting ended 1-1 on Saturday
Jake Cass made it 13 goals for the season as his brace guided Bishop's Stortford to a 2-0 win over 10-man Lewes in the Buildbase FA Trophy on Saturday