For the second successive week, City surrendered a half-time lead at Treyew Road as their National League South play-off hopes suffered another serious blow.
They led relegation-threatened Oxford City 2-0 at half time, through goals by skipper Ben Gerring and Aaron Lamont, but then capitulated in the second period conceding three goals without reply to slump to another deeply disappointing defeat.
Again City began well, taking an early lead when Gerring headed home Connor Riley Lowe’s corner at the far post.
And when Aaron Lamont made it 2-0 with an astute lob over Oxford keeper Craig King, after being put through by Tyler Harvey, they looked on course for a vital three points.
But despite trailing 2-0, Oxford were the better side in the first half and City’s lead flattered them.
The visitors created a number of openings in that first period, with substitute Zac McEachran crashing a shot against the bar and then Godfrey Poku’s follow-up effort was deflected over.
Tom McHale had to save well from Joe Oastler’s header and Riley-Lowe somehow cleared a Frankie Musunda effort off the line.
The closest Truro came to a third was when Harvey was just wide after being slipped in by fellow striker Rocky Neal.
City though as they did against Wealdstone last week at Treyew, then proceeded to fall apart after the break.
Oxford soon pulled a goal back when Austen Booth was adjudged to have fouled McEachran from behind and Matt Paterson converted the penalty.
City seemed at sixes and seven and it was soon 2-2 when the dangerous Samuel Nombe was granted far too much space to find the top corner with a terrific finish.
The home side were shell-shocked and when the normally reliable Jamie Richards disastrously slipped out on the left Nombe took full advantage to race clear and put Oxford 3-2 ahead.
The White Tigers tried to get back into the match without too much conviction, with Ben Harding heading over from a corner and substitute Noah Keats having a shot blocked the closest they came to an equaliser.
But in truth Oxford, who started the day in 17th, were worthy winners with City looking like a well beaten side at the final whistle as the rain poured down.
Truro City (3-5-2): McHale; Gerring (capt), Richards (Thompson 78), Hartridge; Palfrey, Harding, Lamont (Keats 81), Booth, Riley-Lowe; Neal, Harvey (Yetton 88).
Subs (not used): Todd, Copp.
Yellow Cards: Harding, Harvey.
Oxford City (3-4-3): King; Musunda, Oastler, Godwin-Malife; Jones, Fleet, Poku (capt), Grant; Nombe (Fofana 78), Paterson, Sinclair (McEachran).
Subs (not used): Forde.