Glasgow ran in four tries against Ulster on Friday to triumph 20-14 at Scotstoun Stadium, with Niko Matawalu grabbing the crucial score.
In a game played in quite miserable conditions, Ulster made the better start and drove convincingly into the Glasgow defensive line. The early pressure earned its reward, and the away side earned a penalty attempt on three minutes.
Pienaar was uncharacteristically inaccurate with the resultant kick. However the league leaders were establishing an impressive early tempo, and Pienaar made amends by opening the scoring on five minutes following an almighty shove by temporary captain John Afoa.
But the Glasgow response was resolute. The Scottish outfit have established an impressive momentum in the Pro 12 this season and slowly but surely accumulated a succession of phases.
The hosts deservedly managed to get themselves on the scoreboard on 14 minutes, when lock Swinson crashed over for a try in the corner. Glasgow were starting to find a decent rhythm, testing the fringe defence of the league leaders.
It was Ulster who accrued the next scoring opportunity on 17 minutes, however, when Pienaar put the Irish side ahead at 5-6. Glasgow remained the more dominant and physical, particularly at the breakdown.
Ulster's predicament was compounded by a series of inexcusable errors. Seymour restored Glasgow's advantage on 27 minutes, following a horrendous calamity at the base of the Ulster scrum.
Glasgow fly-half Peter Horne missed the conversion, and it was to be a truly forgettable night for the kicker. As well as dominating the physical exchanges Glasgow were looking the more creative behind the scrum; with scrum half Malawahu posing all sorts of problems for the Ulster defence.
Glasgow entered the interval in the ascendancy, having been emboldened by their dominance of the inexperienced Ulster side. If the first half was poor, Ulster started the second period in the worst circumstances imaginable.
Paddy Wallace, who seemed shaken following a bone crunching challenge in the first half, saw his clearance kick charged down and a grateful Murcnhie cantered over for another try.
The vastly experienced Wallace will have been very disappointed with his error. The league leaders were given a reprieve, however, when Horne again missed his conversion. Ulster were now very much playing catch up, and struggled to inject any momentum into their game.
Pienaar did narrow the gap on 48 minutes, to make it 15-9 to the Warriors. But Glasgow remained in the ascendancy, lording it over the Irishmen at the breakdown. The only glimmer of hope came from Ulster's young guns, with their experienced campaigners struggling to assert themselves. It is extremely rare to see Pienaar outplayed by his opposite number.
Ulster did increase their intensity in the final quarter and were offered a lifeline when Stuart Olding scored on 67 minutes. Ulster were now only one point in arrears, and seemed on the verge of securing a win they scarcely deserved. But a resilient Glasgow had other ideas.
The scintillating Matawalu finished off a deserved victory on 72 minutes, when he seized upon an error in Ulster's defensive alignment to seal the bonus point.
Replays revealed that Nigel Owens had missed a forward pass. Horne was again remiss with his conversion. But it scarcely mattered. Glasgow hung on to close out a very impressive victory, secured on extremely solid foundations. Ulster will hope that a season that showed so much early promise is not imploding amid a litany of injuries and lapses in form.
Tries: Swinson, Seymour, Murchie, Matawalu
Pens: Pienaar 3
Glasgow: 15 Peter Murchie, 14 Tommy Seymour, 13 Mark Bennett, 12 Alex Dunbar, 11 DTH van der Merwe, 10 Peter Horne, 9 Niko Matawalu, 8 Ryan Wilson (capt), 7 John Barclay, 6 Josh Strauss, 5 Tom Ryder, 4 Tim Swinson, 3 Ed Kalman, 2 Pat MacArthur, 1 Ofa Fainga'anuku.
Replacements: 16 Fraser Brown, 17 Luke Pettie, 18 Garry Mountford, 19 Nick Campbell, 20 James Eddie, 21 Sean Kennedy, 22 Scott Wight, 23 Graeme Morrison.
Ulster: 15 Ricky Andrew, 14 Michael Allen, 13 Andrew Trimble, 12 Stuart Olding, 11 Neil Walsh, 10 Paddy Wallace, 9 Ruan Pienaar, 8 Robbie Diack, 7 Ali Birch, 6 Conor Joyce, 5 Dan Tuohy, 4 Neil McComb, 3 John Afoa (capt), 2 Nigel Brady, 1 Callum Black.
Replacements: 16 Rob Herring, 17 Ricky Lutton, 18 Andrew Warwick, 19 Alan O'Connor, 20 Mike McComish, 21 Paul Marshall, 22 Darren Cave, 23 Chris Cochrane.
Referee: Nigel Owens (Wales)
by Rory McGimpsey