It was another impressive performance from winger Andy Fenby who put two tries over the line and now jointly leads the Scarlets try scoreboard with five tries from four games - the same as George North.
The older of the two North Walians made the first at 26 minutes look easy - making all running to finish strongly with two defenders trying to keep him from the line. And then just before half-time he capitalised on a mistake by the Treviso full-back Burton who had spilt ball and showed plenty of pace and good footwork to kick forward twice and touch the ball down.
Rhys Priestland had a solid night with the boot with two conversions, one penalty and a drop-goal as well as intelligent kicking from hand well to give the Scarlets momentum, cooly taking with a penalty just after half-time to put the Scarlets 20-5 up.
But the home side, eager for their second win in the competition in front of a lively crowd at Stadio Monigo put in a forceful second half and with the scoreboard at 19-20 in the final quarter , the Scarlets defended courageously for the last 15 minutes, keeping Treviso from scoring on a number of occasions.
The cruel twist at the end was reminiscent of the Scarlets' disappointment in Ulster last season, when Ruan Pienaar ripped them of the lead with a long range penalty just before full-time. And Treviso's Alberto Di Bernardo showed he had the mentality under pressure required to kick a 50m penalty in the last 30 seconds of the game - hearts were in mouths in Italy and West Wales but it went Treviso's way and the home crowd went wild.
Head Coach Simon Easterby said a lot of the Scarlets' hard work and focus in the week leading up to the game had showed in the way they handled the game and that his team lived up to their targets and expectations in terms of physicality and intensity.
??He said: "It was bitterly disappointing for the boys to lose the game in that way, but there's things we can take from this game including how we adapted in key areas of our game up front from the previous weekend. The physicality was much better and the intensity throughout the game was up there throughout.
??"I cannot fault the attitude or effort from the boys, they fought so hard in the second half and with a man down they defended with everything they had.??"We probably tried to create too much at times and later on we played too much rugby in our half and we drew a bit of pressure from their line-out and driving maul.?
"There were also a few instances where our execution and accuracy should have been better.??
"As far as the forwards play went, I thought we competed well against one of the better packs in the league; Treviso are a very physical team and I thought we turned our scrum around this week compared to the previous performance.
??"There were a combinations of factors which led us to lose that game in the end - we just didn't get fully into our game and our stride after scoring a couple of good tries early on.
"It's frustrating that we did not close the game down when we were 20-5 up, it was close quarter stuff in the second half but there were a couple of decisions that went against us and that allowed them field position and momentum with a noisy home crowd behind them.??
"The boys will be feeling it a bit today (Sunday) they really put so much in at the end and the character shown by the team was something which I am sure all our loyal away supporters would have recognised and respected from being there - there were a lot of bruised bodies coming off that pitch on Saturday night and they put themselves on the line to try to hold out a win.??
"We'll be back stronger for the Dragons and it's great to have a big home derby to work towards now on Friday night back at our home; and the chance to show our spirit and ability in front of our loyal Scarlets supporters after these last two games."
The Scarlets are the highest placed Welsh region and sit in second place in the RaboDirect PRO12 league behind Ulster after this weekend.