An early Andrew Trimble try set last season's losing finalists on the way against the team that suffered the same fate 12 months earlier, with further scores from Tommy Bowe, Jared Payne and Dan Tuohy sealing what could be a crucial away triumph.

Trimble, who was picked ahead of Craig Gilroy after the youngster took his place in the Ireland starting side against Argentina, touched down after only nine minutes to give Ulster just the start they were after.

Paddy Jackson was off target with the extras in what proved to be a miserable half for both goal kickers but it made little difference to in-form Ulster.

The young fly-half would also miss a 17th-minute penalty attempt but his woes were minor compared to opposite number Ryan Lamb who failed with three penalties and a drop goal in the opening 40 minutes.

Lamb did close the gap to 5-3 with a successful strike as the game hit the 20-minute mark but Jackson matched his feat three minutes later to re-establish the five-point lead.

Ulster then took the initiative in an 11-minute spell either side of the break as Bowe and Payne both crossed to leave Northampton facing a substantial deficit.

Bowe's 23rd try in his 50th Heineken Cup appearance made it 13-3 on 33 minutes and, even though Lamb struck a second penalty in first-half injury time, Ulster were well in control when New Zealander Payne claimed their third try four minutes after the restart.

The former Auckland Blues full back saw injury rob him of the chance to play his part in Ulster's surge to the Twickenham final in his first season with the province but his maiden Heineken Cup try significantly boosted their hopes of a repeat showing this time around.

Northampton made a whole host of changes in the latter stages after Jackson had missed another penalty but Ulster were good value for the win that pushes them six points clear at the top of the group.

An already impressive showing was given even greater gloss late on as Tuohy powered over for the bonus-point score with just two minutes remaining despite the fact that Ulster were down to 14 men following Iain Henderson's yellow card.

The Saints now slip to third ahead of the demanding return trip to Ravenhill next week as Castres Olympique picked up a second straight European win with a 9-6 victory in Glasgow.