Jared Payne's 77th-minute try secured a crucial bonus point win for Ulster over Treviso to extend their lead at the top of Pool 5.
Tries from Luke Marshall, Craig Gilroy, Robbie Diack and Payne saw a spirited Ulster side take maximum points from their trip to Italy.
Treviso battled away courageously, but never really threatened the Ulster try-line in a dour game played in dense fog. The match was pretty unconvincing as a spectacle, but nevertheless represents a welcome early Christmas present for the Irish province.
The game got off to a busy start; with Ulster doggedly taking their opponents through the phases. And thus it was Ulster that opened the scoring on 11 minutes when Paddy Jackson coolly slotted a penalty that belied the foggy conditions.
Ulster were intent on playing a continuity game, but their efforts were undermined by the poor visibility. Consequently it was difficult for both teams to impose their respective patterns on the game.
The Italian hosts weathered the storm well, and levelled proceedings on 29 minutes through Alberto di Bernardo to level the scoreline it 3-3.
Jackson had a chance to restore Ulster's lead a minute later, but badly scuffed his kick. The Ravenhill men ignited proceedings on the cusp of half time when Irish centre Marshall gathered a kick from Jackson on 37 minutes to touch down.
The TMO adjudged that the try to be good, but his fly-half neglected to add the extras. But he made amends 3 minutes later to make it 3-11 to the Irish province as the teams entered the interval.
The second half began in similar fashion, with both sides struggling to cope with the horrendous conditions. Jackson extended the visitors' lead further on 46 minutes to earn his team an 11-point advantage.
The Belfast side were determined to extend the lead and assert their superiority over the Italian franchise, but struggled to get any real structure into their game. The visitors did breakthrough again on 63 minutes when Irish international Gilroy squeezed over in the corner.
His international teammate duly converted to make it 3-21 to the Irishmen. And the Ravenhill outfit augmented their advantage further on 67 minutes when Diack found himself at the bottom of a maul. Jackson again added the extras, making it 3-28.
The bonus point was now a distinct possibility for the visitors. But conditions deteriorated even further, making protection of the football a thoroughly troublesome exercise. But Jared Payne ensured the perfect denouement for the Irish visitors when he scored the bonus point try after finding himself on the receiving end of a pass from Andrew Trimble.
Jackson added the conversion to make it 3-35. All told, this was a tremendous victory for the Irish side, and they will be particularly pleased with the manner in which they ground out the win in such appalling conditions.
Treviso will be disappointed with a performance and result that failed to showcase their improvement. But Ulster will be delighted with a win that copper-fastens their position at the summit of this group.
Pen: di Bernardo
Yellow Cards: Williams, McLean
Tries: L.Marshall, Gilroy, Diack, Payne
Cons: Jackson 3
Pens: Jackson 3
Treviso: 15 Brendan Williams, 14 Ludovico Nitoglia, 13 Michele Campagnaro, 12 Alberto Sgarbi, 11 Luke McLean, 10 Alberto Di Bernardo, 9 Edoardo Gori, 8 Robert Barbieri, 7 Manoa Vosawai, 6 Alessandro Zanni, 5 Cornelius van Zyl, 4 Antonio Pavanello (c), 3 Lorenzo Cittadini, 2 Leonardo Ghiraldini, 1 Michele Rizzo.
Replacements: 16 Giovanni Maistri, 17 Alberto de Marchi, 18 Ignacio Fernandez Rouyet, 19 Valerio Bernabo, 20 Dean Budd, 21 Paul Derbyshire, 22 Tobias Botes, 23 James Ambrosini.
Ulster: 15 Jared Payne, 14 Andrew Trimble, 13 Darren Cave, 12 Luke Marshall, 11 Craig Gilroy, 10 Paddy Jackson, 9 Ruan Pienaar, 8 Roger Wilson, 7 Sean Doyle, 6 Robbie Diack, 5 Dan Tuohy, 4 Johann Muller, 3 John Afoa, 2 Rob Herring, 1 Tom Court.
Replacements: 16 Niall Annet, 17 Callum Black, 18 Declan Fitzpatrick, 19 Neil McComb, 20 Mike McComish, 21 Paul Marshall, 22 Michael Allen, 23 David McIlwaine.
Referee: Greg Garner (England)
Assistant referees: Steve Lee, Roy Maybank (both England)
TMO: Trevor Fisher (England)
By Rory McGimpsey