Lee Bradbury’s troops dominated the first half in Cornwall but failed to make their pressure count.
The White Tigers came out with renewed purpose in the second half and on 64 minutes grabbed the all-important goal through substitute Tyler Harvey.
It was only a third away defeat all season for the Hawks, who now have a two-point advantage over both Dartford and Hampton & Richmond Borough at the top.
Bradbury chose to rotate his squad – believing they had looked leggy in recent games.
He made four changes to his starting line-up – with Dan Strugnell, Mike Carter, Andreas Robinson and Alfie Rutherford coming in.
Skipper Brian Stock was ruled out by injury.
In a scrappy opening, both the Hawks and Truro were guilty of misplaced passes.
It was the visitors, however, who began to take charge and on 18 minutes went close to breaking the deadlock.
Strugnell cut in from the right and unleashed an effort which rebounded out off the inside of the post.
Jason Prior pounced on the rebound only to see his well-struck shot blocked inside the area.
The Hawks kept up the pressure, with Prior sending another shot whistling past the upright from a good position.
Meanwhile, keeper Ryan Young was a virtual spectator in a half which ended goalless but was played at a good tempo.
Truro created their first chance at the start of the second half from a set-piece.
A free-kick was delivered to the far post where Ed Palmer got between two defenders only to send his header over the bar.
The Cornish outfit were starting to ask a few questions, though, and rocked the Hawks by taking a 64th-minute lead.
Connor Riley-Lowe sent in an inviting cross and Harvey found the net with his header.
In a positive move, Bradbury made a double-change – sending on Matt Tubbs and James Hayter for Rutherford and Fogden.
But boosted by the goal, the White Tigers were playing with a lot more purpose.
Carter forced a full-length save from the home keeper as the visitors fought to get back on terms.
Truro then cleared a Hayter shot off the goalline in the closing minutes to keep the Hawks at bay.
Hawks: Young, Strugnell, Williams, Woodford, Harris, Rose, Carter, Fogden, Robinson, Prior, Rutherford. Subs: Tarbuck, Lewis, Hayter, Tubbs, Dudzinski