Neither defender appeared troubled on their returns from injury as this FA Premier Reserve League clash went from dour in the first hour to an exciting final third that climaxed with Jackson's sublime goal in injury time.
The first hour was instantly forgettable in miserable conditions at Vicarage Road with rain lashing down and wind swirling.
Watford came closest in the first half when Hameur Bouazza hit the post in the sixth minute.
We controlled possession but didn't really get anywhere while the home side broke at pace but couldn't break down an experienced defence that included Edman, Gardner and Mauricio Taricco.
The game came to life on the hour though as we carved out two chances in as many minutes with Mark Yeates and Eddie Silva Sousa just wide of the mark.
However, we took the lead from the second of those chances as Alec Chamberlain deflected Silva Sousa's effort wide and from Yeates' corner, Marcus Gayle headed into his own net.
Jamie Slabber, Silva Sousa and Spase Dilevski all tried their luck as we got on top but somehow Watford pulled level with their only chance of the half.
The lively Anthony McNamee curled in a corner that Marton Fulop didn't deal with, Taricco cleared one shot off the line, the follow up was goalbound again, Marcel McKie tried to clear, it struck the hand of Hand - Jamie Hand - and went straight in. The goal stood under protest and it looked like being a frustrating night.
That sense of frustration grew when Silva Sousa hit the inside of the post with five minutes left but just as it looked like a draw, Jackson produced his moment of magic.
It was a classic breakaway goal with Yeates picking up the ball on half-way and delivering the perfect pass for Jackson. The midfielder took it in his stride, flicked it around the last defender and coolly lobbed over Chamberlain from 18 yards. A goal worthy of winning any match.
GUIDE TO THE ACTION
6mins: WOODWORK. Watford broke our possession down in midfield, one pass and Bouazza was through on goal, Fulop stood up well and deflected shot onto post.
8mins: Great cross on the run from Dilevski heading for Yeates at far post but Collins just able to knock ball away on the slide.
36mins: Best move of half involving Gardner, Jackson and Dilevski ended with Jackson's shot on penalty spot deflected just wide by fine tackle from Gayle.
45mins: Diagouraga shot from the edge of the box flew over.
Half-time: Watford 0, Spurs 0
60mins: CHANCE. Quick feet from Yeates took him past two challenges and into box but screwed shot wide from 12 yards.
62mins: SAVE. Almost identical chance for Silva Sousa, onto Hughes' pass, into box, right side, aimed at far post, deflected wide by Chamberlain.
63mins: GOAL. Yeates in-swinging corner headed into own net by Gayle.
Watford 0, Spurs 1
73mins: Slabber into box, left channel, under pressure, got shot off but dragged wide.
80mins: Skills from Silva Sousa cutting in from left, fed Dilevski, shot straight at Chamberlain.
81mins: Silva Sousa worked a yard on edge of box, decent strike straight at Chamberlain again.
82mins: Rare shot at goal from home side, Hand's ambitious 30-yarder gathered easily by Fulop.
84mins: GOAL. Slightly controversial equaliser. Fulop failed to deal with McNamee's inswinging corner, first effort in scramble cleared off line by Taricco, follow up again heading for goal, McKie's attempted clearance struck arm of Hand three yards out and went straight in.
Watford 1, Spurs 1
85mins: WOODWORK. Silva Sousa effort from 10 yards hit inside of post and out to safety with Chamberlain well beaten.
Injury time: GOAL. Classic counter attack to win it. Yeates picked out perfect pass for Jackson who nipped the ball around the last defender before superbly lifting ball over Chamberlain and home off the underside of the crossbar.
Watford 1, Spurs 2
Line-ups: Watford: Chamberlain, Herd, Collins, Hand, Mayo, Gayle, McNamee, Fitzgerald (Grant, 84), Bouazza (Diafutua, 60), Diagouraga, Ferrell (Gilligan, 75). Unused subs: Kirk, Mariappa.
Spurs: Fulop, Taricco, Edman (McKie, 63), Hughes, Gardner (O'Donoghue, 75), Defendi, Dilevski, Jackson, Slabber, Sousa Silva, Yeates. Subs: Forecast, O'Hara, McKenna.
Erik Edman completed an hour and Anthony Gardner 75 minutes as Johnnie Jackson's superb late winner made it six wins in seven for our reserves at Vicarage Road on Wednesday night.