Two first-half goals fired Tonbridge into the Bostik Premier play-off final on Thursday night.
Angels had Adem Ramadan and Chinedu McKenzie to thank before they somehow survived a second-half onslaught from the home side.
It means they now have home advantage in Monday's final when they will host Merstham at Longmead.
As expected, Tonbridge boss Steve McKimm recalled James Folkes, D'Sean Theobolds and Tom Derry to his starting line-up.
Heavy rain prior to the game meant a slick 3G playing surface and Angels took full advantage, settling early on after offering up an early chance to Haringey forward Kudus Oyenuga, who lacked power from 20 yards.
Man-of-the-match Theobolds set the tone, creating space with some neat footwork before seeing his low sixth-minute drive turned behind by keeper Valery Pajetat.
McKenzie latched on to a header forward but was also denied by Pajetat inside the opening 10 minutes.
Joe Turner is Angels' player-of-the-year but it was the visitors' other winger, Ramadan who stood out.
He caused all manner of problems for left-back Michael O'Donoghue. Ramadan skipped past his man after 15 minutes but saw his left-foot curler come back off the post, Derry tucked away the rebound but was thwarted by the offside flag.
At the other end, Lyle Della-Verde was denied by the legs of Jon Henly but it was a rare attempt on goal from the hosts who started the game with just one up front.
Angels were rewarded for their inventive play with two goals in eight minutes before the break.
A quickly-taken corner caught the hosts napping and Ramadan picked his spot from the angle of the penalty area on 35 minutes.
Then the visitors countered from a Haringey corner with a three-on-one break. The ball in from Derry was blocked, but it fell perfectly for McKenzie, who drilled into the far corner from 20 yards.
Haringey had to show some ambition after the break and they pulled a goal back just two minutes after bringing on a second striker.
Della-Verde looked to have overrun the ball as he burst into the penalty area, but he went down with Turner alongside him.
Referee Andrew Humphries, who had a decent game overall, amazingly gave the spot-kick and Oyenuga slotted home to make it 2-1.
Indeed, before he was replaced midway through the half Oyenuga should have made it 2-2 but he somehow blazed over from eight yards after intelligent play by Joel Nouble.
Chinedu nearly gave Haringey a helping hand when he gave the ball away cheaply and after a swift break it needed an excellent block by Folkes to deny Nouble, with Craig Stone back on the line to hack the ball clear.
Henly was then on hand to deny Della-Verde at his near post as the hosts really put Tonbridge under pressure.
Haringey had two more chances to force extra-time but defender Coby Rowe, who played as a third striker for the final five minutes, saw his 90th-minute shot come back off the crossbar before being cleared to safety.
Then Della-Verde was played in but he turned his shot wide of the upright with just Henly to beat as substitute Jared Small got back to challenge.
The final whistle sparked wild celebrations from the visitors, who enjoyed their success with a strong travelling support who - like their home counterparts - were in good voice throughout.
Haringey: Pajetat, L Stone, O'Donoghue, Djassi-Sambu (Akinwande 53mins), Richards, Rowe, Della-Verde, Aresti, Oyenuga (Froxylias 66mins), Staunton, Nouble. Subs not used: McDonald, Kirby, Byfield.
Tonbridge: Henly, Folkes, Parter, Theobolds, Miles, Lee, Ramadan (Small 75mins), Stone, Derry, McKenzie, Turner (Read 84mins). Subs not used: Smith, Adonis-Taylor, Ibrahim.