ONE moment of stupidity was all it took to turn Glasgow from a side battling their own gremlins to one overpowered and, in the end, over-run by an Ospreys side who managed to add the embarrassment of scoring a try bonus in their first win at Scotstoun.

The moment that swung the game as a contest came early in the second half when Brian Alainu’uese, the big New Zealand lock Glasgow signed last month to cover a swathe of injuries, charged into a ruck, his shoulder hitting Rory Thornton, his opposite number, on the head.

What made it particularly ridiculous was that his team were under no real pressure at the time so he had no need to go overboard in the way he did, particularly only a couple of weeks after the rugby authorities put out an edict ordering referees to clamp down on that kind of collision.

"We normally watch the game back three or four times and on that incident I won't want to comment until I have seen it back," said Gregor Townsend, the head coach. "Obviously it was a big moment in the game when you lose a player, especially in a game that is so tight and it is a player who is so crucial in scrum and line out."

At the time, Glasgow were trailing by five points but once a man short they were over-run by the Ospreys who scored three more tries and would have won even more comfortably if Josh Matavesi, their Fijian fly half, had been able to concert more than one of them and miss a penalty as well.

Even with Alainu’uese on the field, Glasgow could not put their game together as they struggled to cope with the loss of 18 players away with international squads. Since the Ospreys had nine off with Wales, it was effectively a clash between two second string sides with a few more experienced players asked to raise the standard.

The teams came into the match level on points and separated only on score difference. With Ulster's game being called off because of the frost in Belfast, there was a chance to open daylight from the chasing pack, but the result puts Glasgow down to fifth in the PRO12, while the Ospreys move up to second.

Predictably, as the side closer to full strength, it was the Ospreys who clicked first, dominating the early possession and territory. They struggled to get past the Glasgow defence, though and when Josh Matavesi, the fly half released by Fiji to play, missed a penalty they still had nothing to show for their effort.

Instead it was Glasgow who had the first scoring chance as Lee Jones, the wing, latching on the ball as it went loose after a kick, only to be hauled down five yards short after deciding to go on his own rather than use the support inside him.

That brief flurry of excitement out of the way, they soon got back to the main theme of the night, making mistakes. So it was entirely appropriate that it was a catalogue of blunders that led to the only score of the first half.

With the ball squirting around outside a ruck, four players managed to miss it, handing it to Daf Howells, the wing, who hacked upfield to set up a race between Tom Habberfield, the scrum half, and Nick Grigg, the Glasgow centre. Even though TV pictures seemed to show they both got to the ball at the same time the try was awarded.

That was all that separated the sided at the break but it all swung to the Ospreys in the second half as Matavesi took advantage of the attacking platform from the red-card penalty to put in an inch-perfect cross kick for Tom Flaherty to score on the wing.

By now the Ospreys forwards were dominating the game and they drove Dan Baker, the No8, over for the third try before creating the space for Ashley Beck, the centre, to score half way out.

Glasgow did have a late flurry and avoided the embarrassment of finishing scoreless when Junio Bulumakau, the replacment wing, was put over in the final minutes but it was only a tiny boost.

Glasgow Warriors: Try: Bulumakau

Ospreys: Tries: Habberfield (37), O'Flaherty (49), Baker (58), Beck (67). Conversion: Matavesi

Scoring sequence (Glasgow Warriors first): 0-5 (half time), 0-10, 0-15, 0-22, 5-22.

Glasgow Warriors: P Murchie; S Lamont, N Grigg, S Johnson (P Kelly, 69), L Jones (J Bulumakau, 73); R Clegg, G Hart (G Horne, 70); G Reid (R Grant, 55), C Flynn (P MacArthur, 55), D Rae (A Nicol, 21-26, 59), T Swinson, B Alainu’uese (send off: 47), L Wynne, C Fusaro (L Haupeakui, 58), J Strauss (C) (R McAlpine, 74).

Ospreys: D Evans; D Howells, K Fonotia, A Beck (L Price, 73), T Grabham (T O'Flaherty, 43); J Matavesi, T Habberfield (C) (B Leonard, 67); P James (G Thomas, 73), S Parry (S Otten, 58), M Fia (R Jones, 54), L Ashley (A Beard, 69), R Thornton, O Cracknell, S Underhill (R McCusker, 66), D Baker.

Referee: G Clancy (Ireland)

Attendance: 7,166