Pool 5 is the tightest of four-way struggles and, if this game is anything to go by, there will be a few more twists and turns of the tourniquet yet. Let's hope they deliver as much pleasure as this did. Not that either team seemed particularly overjoyed with the outcome, but that is the luxury of being an observer in this competition. The tribulations of the gladiators as they strive for every last morsel of advantage are not for them to enjoy.

Saracens have been unconvincing of late, but they exploded into this one. Maybe calling Wembley your home, even if only for the odd day here and there, can do this to a team. Being able to call anywhere their home is still a touchy subject with the English champions, but here the players seemed to be voting with the level of their performance.

The home side played what they felt were the best 50 minutes of their season, opening up a 28-16 lead with half an hour to go. They might reasonably have felt that the pool was all but theirs if they could just score a fourth try for the bonus point. Instead, it was the Ospreys who waxed in the final half-hour and the bonus point ended up theirs. A precious edge as the teams march on to the return fixture in Swansea on Friday night.

But the Welshmen might easily have had that bonus point taken away. Having swept their way to a second try on the hour to bring themselves within five points, they gifted Saracens an attacking scrum in the 72nd minute. As he had done all afternoon, the referee took exception to something the Ospreys did at that set piece and a simple penalty took Saracens back out to eight points. Fortunately for the Ospreys, they won a penalty almost immediately, when Rhys Webb charged down Owen Farrell's clearance from the restart, precipitating a scramble for the ball.

Scott Johnson, the Ospreys' director of coaching, was livid that the bonus point had so nearly been taken away by something as inscrutable as a scrum interpretation. "I'm no scrum guru," he said, "but I can tell you the illegalities were not all one way.

"The scrum here has become a lottery. We may as well just sit there and toss a coin. 'Whose turn is it going to be this time [to be penalised]?' We've got to do something about the scrums, because it's becoming farcical."

The Ospreys, if they were of a mind to, might also have complained about the second Saracens try. It seemed a bit early for big turning points, but a breathless opening quarter of an hour culminated in a try for Saracens to open up a 17-10 lead. The Ospreys had just settled into their rhythm, after Saracens had torn into them from the off, Rhys Gill driving over for their first try in only the third minute. The Welshmen managed to level things at 10-10 when they scored their first try 10 minutes later, Ashley Beck creating and finishing the first of his brace.

The visiting ship seemed righted, and soon Shane Williams was twinkling away from his own 22. But he was called back when the referee adjudged one of two decent-looking passes forward and the Ospreys were introduced to the first of their set-piece woes. Ernst Joubert burst from the base of the subsequent scrum through Tom Smith's feeble tackle and on to the tryline.

It was not a happy day for Smith, the Ospreys captain. Five minutes before half-time, he saw yellow for recklessness at a rolling maul and, by the time he returned in the second half, Saracens had opened up that 28-16 lead, courtesy of Chris Wyles's try.

But then it was Saracens' turn to suffer at the hands of the referee. Farrell body-checked Dan Biggar after the Ospreys fly-half had chipped ahead and off he went to the sin bin. By the time he returned, Beck had gone over for his second, after Biggar had sent the impressive Richard Fussell on a run.

Saracens now seemed to be fading, but Biggar got a bit carried away when he passed to Andrew Bishop in front of his own posts, and the centre slipped. That coughed up the five-metre scrum that so nearly cost the Ospreys their bonus point. There was enough life in them, though, to win that last crucial penalty. As a result, there is quite a bit of life left in what is turning into a vintage pool.