Glasgow stretched their winning run in the Pro12 to five games with an engrossing comeback against Ulster at Scotstoun.
The visitors scored the first two tries of the match, early in the first half through Iain Henderson and early in the second with a controversial one for Stuart McCloskey.
Glasgow trailed 17-9 after almost an hour, but rapid-fire scores from man-of-the-moment Stuart Hogg and then Tommy Seymour dealt a blow to Ulster’s play-off hopes.
Ulster were even denied the consolation of a losing bonus point when Hogg, the great showstopper, boomed over a penalty from 53 metres with the last kick.
The drama – and the big refereeing calls from John Lacey – began as early as the second minute when Glasgow lost the golden boy of Scottish rugby, Hogg, to the sin-bin. The full-back came in at the side of a ruck and while he was away, Ulster struck.
It had been on the cards even with a full complement, as Ulster carved Glasgow open in those opening minutes, with Stuart Olding and Craig Gilroy’s footwork getting through soft tackling from the home side and into open country.
The try when it eventually came was richly deserved, Olding throwing an inside pass for Henderson to score under the posts on his return to action after four months out injured.
Paddy Jackson’s conversion made it 7-0 to the visitors in a city where they have lost their previous five games in the Pro 12, most notably the two-point loss in last season’s semi-final.
Glasgow finally found some belligerence midway through the half. Their big carriers took them into Ulster territory and the visitors were penalised repeatedly at the breakdown.
Two Russell penalties made it 7-6 after the half-hour before two more penalties – one apiece for Jackson and Russell – left it at 10-9 to Ulster at the break.
Lacey had been a deeply unpopular character with the Glasgow supporters in that opening half. The breakdown had been a shambles and the home crowd, unsurprisingly, laid the blame squarely at Ulster’s door.
Their ire turned to blind fury when McCloskey scored early in the new half. From a downfield kick to touch, Ulster took a quick throw – from Gilroy to McCloskey – who crashed over while Glasgow dozed.
The controversy arose over whether the ball travelled the requisite five metres and the fact Lacey decided to forego the TMO and award the score. When Jackson converted, Glasgow trailed 17-9.
Their response was magnificent. First, Hogg chipped over Olding down the left wing and ran on to gather and score for a classic predator’s try. Then, Russell’s crossfield kick was taken at full pelt by Seymour, who belted away for Glasgow’s second try.
Russell converted and, suddenly, Glasgow led 21-17. They had to soak up pressure after that with questions asked of their defence -which were soundly answered.
When Russell put over a penalty for 24-17 with seven minutes left, the game was as good as up.
The last act belonged to Hogg, who launched a 53-metre penalty to deny Ulster a losing bonus.
It was a precious victory for the defending champions, whose momentum is growing all the time along with their prospects of retaining their crown.
Glasgow: S Hogg, T Seymour, M Bennett, A Dunbar, S Lamont, F Russell, H Pyrgos; G Reid, F Brown, S Puafisi, J Gray (capt), L Nakarawa, R Harley, C Fusaro, J Strauss.
Replacements: J Malcolm, J Yanuyanutawa, Z Fagerson, T Swinson, R Wilson, G Hart, D Weir, T Naiyaravoro.
Ulster: S Olding, C Gilroy, L Marshall, S McCloskey, R Scholes, P Jackson, R Pienaar; C Black, R Herring (C), R Lutton, A O’Connor, F van der Merwe, I Henderson, C Henry, N Williams.
Replacements: J Andrew, K McCall, A Warwick, R Diack, S Reidy, P Marshall, S Windsor, D Cave.