In a game they led until eight minutes from time, Ulster's Champions Cup campaign got off to the worst possible start with a 28-13 defeat to Bordeaux-Begles in France.
Having taken the lead in the first-half through their returning skipper Andrew Trimble's score, Ulster spent the second 40 clinging on by their fingertips to a slender advantage but after a late capitulation they returned home without even the consolation of a losing bonus-point.
Bordeaux scored three tries in the closing minutes while Ulster spurned the chance of at least taking something from the game when they ignored a simple shot at the posts in the final seconds despite trailing by more than a converted score.
Les Kiss's side lacked composure in the opening minutes, as shown by an uncharacteristic off target pass from Pienaar that put Jackson (right) under pressure and, as early as the third minute, Ian Madigan was handed the first chance for points when Ulster were pinged for not releasing.
He duly delivered and Ulster were caught cold by their opponent's quick start for a third week in a row. This time, however, they adjusted to the contest's frenetic pace and were quickly in the ascendancy.
On a surface that was cutting up with every scrum - Ulster defence coach Joe Barakat had highlighted concerns during the week that the Stade Chaban-Delmas pitch was not fit for purpose - the visitors still managed to play some enterprising rugby and took the lead in the 22nd minute.
With Bordeaux wing Blair Connor dropping back to cover a kick in behind, he was swallowed up by Trimble, Craig Gilroy and Clive Ross to give Ulster an attacking scrum.
Stuart Olding carried and, with men to Pienaar's left, the returning Trimble ran a strong line against the grain to receive an inside ball to score.
The wing was clearly enjoying his afternoon back in the side, flying up out of the line to smash Romain Lonca minutes later when Madigan telegraphed his flat pass.
In Ulster's best spell of the contest, there were further chances before half-time. Trimble and Jackson were inches away from linking up in the corner while one ball was fumbled forward inside the '22', but they had to make do with only a penalty after Sean Reidy earned Jackson a shot at the posts.
The second-half began much in the same vein as the first, Madigan slotting an early penalty with his side very much on top, but where Ulster came back to enjoy a purple patch of their own before, this time it was all Bordeaux.
The French forwards racked up phase after phase deep in Ulster territory for what must have felt like an eternity but, until the late scoring flurry, had been held at arms length by determined work at the breakdown and spilling of the ball.
Indeed, when Iain Henderson ripped the ball free close to his line and Ulster won a penalty during their next attack, it seemed an important moment after Jackson's sweetly struck effort from inside his own half bisected the posts.
Even when French international prop Jefferson Poirot earned a scrum penalty that substitute Lionel Beauxis knocked over with 25 minutes remaining, Ulster still led by four points.
They would hold onto the advantage until the defining final ten when Bordeaux's superiority eventually told.
After Ulster's exit strategy malfunctioned horribly when the ball squirted loose beyond their own line, Jackson's clearing kick was blocked and the Top14 side were awarded a penalty five metres out. With their forwards going to the well once more, this time they did muscle their way over when replacement prop Sebastien Taofifenua shrugged off the Ulster attempts to push him into touch with a forceful finish.
The missed conversion would leave Ulster only a point behind but another almighty mess at the restart saw Metuisela Talebula scamper up the wing and offload for Baptiste Serin. While he was unable to finish, JP Doyle adjudged that Sean Reidy had made the tackle early and awarded both a penalty try and a yellow card.
The subsequent conversion left Ulster trailing by eight and unable to win the game in the final minutes, but a penalty sent into Bordeaux's half gave a rare chance for a score that would have brought at least a consolation of a bonus point.
Whether the speed with which the complexion of the game had changed affected Ulster, the maths appeared to elude the side when they went for a quick tap instead of the posts when Bordeaux transgressed again.
When Trimble lost the ball in contact, it was then relatively academic that his opposite wing Blair Connor was allowed to scamper home untouched but, for a side who missed out on the quarter-finals of last season's competition by a single point, the importance of surrendering that losing bonus point from such a position should need little highlighting.