Exemplary goal-kicking from Ruan Pienaar topped up tries from Nick Williams, Jared Payne and Darren Cave, and with Castres Olympique falling 18 - 12 to Northampton Saints at Franklin's Gardens, Ulster are now guaranteed to progress to the knock-out stages - although a home quarter final is still to play for in next Saturday's clash in the south of France.

Mark Anscombe's side was bolstered by the return of the in-form Jared Payne at full-back, while Paddy Wallace reclaimed the number 12 jersey after the injury sustained by Luke Marshall in last Friday's defeat of the Scarlets. Three further changes among the forwards saw Rory Best reinstated at hooker, John Afoa start at tighthead, and Iain Henderson claim his 11th cap in the second row, with Dan Tuohy sidelined due to a calf strain. Notable also tonight was Andrew Trimble's 150th appearance in the white and red jersey.

After a disjointed opening five minutes punctuated by several knock-ons of a slippery ball by the Warriors, Pienaar opened the Ulster account with a penalty from outside the '22', just before the rainfall escalated to a torrential level. The increasingly difficult playing conditions soon put paid to any hopes either team had of producing truly constructive rugby at this stage, although a smart kick from Cave into the corner on 18 minutes almost set Trimble away, before Peter Murchie scampered back to kick into touch.

Ulster worked the lineout well, powerfully driving ever closer to the line until crowd favourite Williams took over with a metre to go and barged over for the try. Pienaar added the extras for a score of Ulster 10 Glasgow 0 at the close of the first quarter.

A second Pienaar penalty attempt span wide five minutes later, and the very next manoeuvre almost saw the registration of the second home try, as Glasgow inexplicably surrendered the ball under no real pressure in their own '22' - but here, once again, the greasy ball undid the attack, as Ulster fumbled on the right wing. The half then closed on two errant Duncan Weir penalty attempts, ensuring Ulster went in at the break with their scoresheet intact.

Half-Time Score Ulster 10 Glasgow 0

With the rain at a more manageable level as the second half began, Glasgow started to edge their way into the encounter, and were well worth the three points struck by Weir's boot on 47 minutes. The Scots continued to enjoy the lion's share of possession and, with Henderson sinbinned for an offence in the ruck on 52 minutes after a succession of Ulster transgressions, the visiting out-half kicked a further three from close range to bring his team within touching distance at Ulster 10 Glasgow 6.

Paul Marshall and Roger Wilson made their entrance on the hour mark in lieu of Paddy Jackson and Robbie Diack respectively, Pienaar and Williams moving to out-half and blindside as a result. The Springbok restored Ulster's seven-point cushion on 62 minutes courtesy of a central penalty, then only just failed to extend it to 10 moments later after Glasgow had been pulled up for infringement at the scrum.

It mattered little, however, as the definitive breakthrough came on 73 minutes, Payne touching down in the right-hand corner after Ulster's most fluid collective move of the match, with good work from Marshall in particular to extract the ball from several congested mauls before spreading play wide. Pienaar was then unlucky to see his conversion attempt rebound off the upright from a tight angle on the right flank.

The highlight of the match came with two minutes remaining, when, with the contest won and many of the 10,940-strong crowd already making their way to the exit, Cave capped a strong personal performance with a virtuoso solo try. Picking up on the left wing with a lot of work to do, the centre danced his way past a handful of lunging challenges with all the finesse of a world-class wing, before cutting inside to evade several more men, and sliding over the whitewash under a final despairing tackle. With only seconds now left on the clock, Ulster made a last-ditch attempt to secure the fourth try and bonus point, which unfortunately came to naught as time ran out.

With one round of pool matches remaining, Ulster now sit on 19 points, five clear of Saints and six ahead of next weekend's opponents Castres. Although qualification is now a certainty, a good result in France next week would secure the inestimable advantage of a home draw in the quarter-final.

Full-Time Score Ulster 23 Glasgow 6

Ulster
(15 - 9) J Payne; A Trimble, D Cave, P Wallace, C Gilroy; P Jackson, R Pienaar
(1 - 8) T Court, R Best, J Afoa, L Stevenson, I Henderson, R Diack, C Henry (c), N Williams
Replacements (16 - 23) R Herring, C Black, D Fitzpatrick, N McComb, R Wilson, P Marshall, M Allen, C Cochrane

Glasgow
(15 - 9) P Murchie; S Maitland, A Dunbar, P Horne, DTH van der Merwe; D Weir, H Pyrgos
(1 - 8) R Grant, D Hall, M Low, T Ryder, A Kellock (c), J Eddie, R Harley, J Strauss
Replacements (16 - 17, 19 - 23) P MacArthur, G Reid, N Campbell, T Swinson, N Matawalu, S Wight, S Hogg