A try by visiting stand-off Paddy Jackson just after the hour-mark proved to be the winning strike on a night when Gregor Townsend’s men suffered a series of injuries.
Glasgow were looking for three in a row over Ulster at Scotstoun but knew that, in the last two meetings here, back in March and in the previous season’s Pro12 semi-final, they had had to dig themselves out of holes before assuring the victories.
Again it was the Ulstermen who started the strongest as the heavens opened right on kick-off and Jackson gave them the lead in six minutes with a long-range penalty having previously missed with an earlier effort.
Ulster thought they had added a try to their total when Jared Payne burst through but it was ruled out due to an illegal clear-out by Iain Henderson, who was yellow carded.
However, the visitors remained on the front foot despite the numerical disadvantage and did register the first touchdown of the evening in the 18th minute when Darren Cave had the easiest of jobs of finishing off in the right-hand corner after the Warriors defence had been stretched to its limit.
Jackson missed the conversion and Glasgow hit back within four minutes when a concerted push on the Ulster line bore fruit when prop Gordon Reid crashed over. Finn Russell, pictured, who was celebrating his 24th birthday by making his Warriors return after spending four months out following a bad head knock sustained in last season’s Pro12 semi-final at Connacht, added the extras to make it a one-point game.
Townsend then had to shuffle his pack when lock Greg Peterson was forced off injured in the 22nd minute. Former All Black Corey Flynn, who was a late call on to the bench in place of Pat MacArthur, came on at hooker, with Fraser Brown moving back to his old back-row position.
There were more changes as Reid departed for a head injury assessment and was replaced by Alex Allan and then Namibian international Tjiuee Uanivi, who had moved up to second row in the reshuffle, had his first start for the club cut short to make way for a debut in the shape of young replacement Sam Thomson.
Ulster had another try, perhaps harshly, chalked off just after the half-hour mark for alleged obstruction by tighthead Rodney Ah You, who was in front of the drive dragging hooker Rob Herring over the line and blocking a tackling opportunity.
The province continued to be the dominant force in the game approaching the break and were rewarded in the 39th minute with a penalty try, after Italian wing Leonardo Sarto was adjudged to have tackled the always menacing left wing Charles Piutau without use of the arms and Jackson converted to make it 15-7 at the interval.
After Tommy Seymour had pulled off a brilliant tackle to dislodge the ball just as Jackson looked certain to score and strike a decisive blow for Ulster, Russell pegged back another three points with the boot in the 47th minute.
Nine minutes later, Glasgow got themselves ahead for the first time when the brilliantly elusive Stuart Hogg opened the door for Seymour to get over in the right corner for his seventh try of the season and Russell nailed a brilliant touchline conversion.
The lead didn’t last long, however, as Jackson finished off a slick passing move by Ulster and converted to restore a five-point advantage for the Irishmen.
Glasgow had their moments of pressure in the closing stages and threatened to strike back but Ulster did well to contain them and ended the stronger side to see out a deserved victory.