A tight and fiercely contested first half, in plunging ice-cold temperatures, saw Cardiff Blues take a slender one-point lead into the break courtesy of a try from USA international wing Blaine Scully.
Back came Treviso and a penalty try early in the second half gave them the advantage they craved as they then hung onto despite wave after wave of visiting pressure.
Even a late surge camped in the home 22 from Cardiff Blues failed to muster a match winning score - with Manoa Vosawai twice held up on the line - and Head Coach Danny Wilson was left to rue a missed opportunity to climb the league table.
Wilson had made three changes to his side as centre Cory Allen and hooker Kristian Dacey returned from Six Nations duty with Wales while Under-20s playmaker Jarrod Evans was selected at fly half.
In freezing temperatures it was the home side that were running red-hot in the opening minutes as Cardiff Blues were given a stern examination from the kick-off.
A big overlap saw Dan Fish fly out of the line and stop what looked a certain try as he wrapped his man up, but with a penalty already secured for offside it was home full back Jayden Hayward that opened the scoring.
Number Eight Vosawai, up against his old club, and the returning Dacey looked to instigate a response while Patchell arched a neat run from deep to open up space in midfield.
But it was a rare foray into home territory and Treviso looked the more threatening as centre Luca Morisi broke away from tacklers but his floated pass wide right found a retreating Fish and not supporting runners.
A scuffed penalty from Hayward, that just about found its way over the bar after another penalty for offside, extended the advantage for the Italians, who were good value for the lead.
A first real attack of note from Cardiff Blues at the mid-point of the half saw Patchell kick to the corner after a penalty was secured at the breakdown.
The forwards rumbled up close with a driving maul, but when the backs took over they failed to find any cutting edge as Allen and Fish both looked to roll out of tackles in adversity.
A big defensive shift from Cardiff Blues was still required as Samoa centre Rey Lee-Lo unloaded a huge tackle to turn over possession and then teamed up with Ellis Jenkins to disrupt home play on halfway.
Some neat phase play almost brought reward for Fish over out wide before a free kick against Treviso, for delaying a lineout, saw the visitors strike with a clinical move.
The forwards twice went close, with captain Jenkins leading the way, before the ball was spun right down the line and Allen and Patchell combined to send Scully over in the corner for game’s first try five minutes before the break.
A big scrum on the stroke of half-time won another visiting penalty and one last attack with seconds left. But, after securing the ball and driving on, the chance went begging as Cardiff Blues infringed at the breakdown.
The visitors were made to pay for not taking advantage just minutes after the restart as Treviso won a scrum five-metres out and never looked like getting the ball away from the set piece as they repeatedly applied pressure.
Two infringements later the referee was under the posts to award a penalty try for dragging the scrum down and Hayward’s extras make it 13-7 with half an hour to play.
As the second half wore on the heavy pitch started to take its toll on the battling Italians, who were now having to defend for long periods as Blues started to dominate territory.
Wing Scully broke down the right flank, as he stepped his opposite man, before replacement scrum half Tomos Williams looked to support him but was bundled into touch.
Aled Summerhill was next to try and break Treviso resolve down the left, as he burst past the first tackler, before hooker Ethan Lewis brushed off two tackles and rattled up the middle. Ball was recycled quickly and spun wide, but Vosawai was held up as he stretched for the whitewash.
A series of scrums and penalties eventually came to nothing, as spilled ball saw the chance lost, before a final five minute siege saw Vosawai again adjudged to have not grounded the ball as he burrowed for the line.
The home scrum was now being shunted around at will, but one last attack saw the visiting forwards held up short before Scully was forced out as the final whistle sparked wild home celebrations.
Timeline:
09m Hayward p 3-0
22m Hayward p 6-0
35m Scully t Patchell c 6-7
49m Penalty t Hayward c 13-7
Cardiff Blues: 15 Rhys Patchell, 14 Blaine Scully, 13 Cory Allen, 12 Rey Lee-Lo, 11 Dan Fish, 10 Jarrod Evans (Summerhill 62), 9 Tavis Knoyle (Williams 53); 1 Thomas Davies (Thyer 65), 2 Kristian Dacey (E Lewis 65), 3 Salesi Ma’afu (Filise 49), 4 Jarrod Hoeata (Reed 65), 5 James Down, 6 Josh Navidi (Cook 73), 7 Ellis Jenkins, 8 Manoa Vosawai
Replacements: 16 Ethan Lewis, 17 Bradley Thyer, 18 Taufa’ao Filise, 19 Lou Reed, 20 Macauley Cook, 21 Tomos Williams, 22 Garyn Smith, 23 Aled Summerhill