There are days when good guys do come first and yesterday at Vicarage Road was one of them. A day when the belief and generosity of Nigel Wray, the Saracens benefactor whose faith has been so sorely tested in the past 12 years, was rewarded and when Richard Hill found himself in a European semi-final for the first time since he became a Saracen in 1992.

Few would have given England a representative in both the Heineken Cup semi-finals this season, such is the uneven form so many clubs have shown in the Guinness Premiership. Yet two newcomers to the knockout phase are there: London Irish will grace Twickenham against Toulouse on April 26, while, a day later, Saracens will take on Munster at the Ricoh Arena in Coventry, thanks to a performance against the Ospreys drawn deep from their well of self-belief.

A fortnight earlier, Saracens had crept quietly away from Cardiff's Millennium Stadium beaten 30-3 by the Ospreys in the semi-finals of the EDF Energy Cup and yet Ryan Jones, the Wales captain, had emphasised last week that this was a new competition, a new match. How right he was: the Ospreys, hailed by many as the most likely winners of the Heineken Cup this season, were flat and slipshod amid the snowy Hertfordshire wastes.

Saracens' set-pieces worked far better (the Ospreys did not win a scrum until six minutes before the interval) and the international pairing of Justin Marshall and James Hook failed to function. It is rare for Hook to have so poor a day, but the fly half kicked badly, took no notice of gaps as they opened up and almost created a try for Saracens just before the interval when he compounded a missed catch with a missed clearance.

“On a club level, this is up there with the best of them,” Hill, the former England flanker who retires at the end of this season, said. “Many people laughed at Nigel [Wray] when he became involved and said he wanted to see a packed Vicarage Road watching Saracens on the European stage, and now he has. People have asked me why I've gone on this long but it's for days like this, that feeling of elation at the end of the match.”

It becomes no easier for Saracens, who play Gloucester and London Wasps in the Premiership in the next two weeks before Alan Gaffney, their director of rugby, prepares the side against Munster, where he spent three years. They will be without Andy Farrell, the England centre who has ruptured his acromioclavicular joint in his shoulder and will be out for three months, while Brent Russell and Paul Gustard must recover from hamstring and shoulder damage respectively.

Yet the loss of such experienced individuals only showed how tight a unit Saracens have become: Adam Powell hurled himself into the fray and Francisco Leonelli scored the game-breaking try at the start of the second half. Saracens felt aggrieved not to be leading by more at the interval: Hook's early penalty goal had been erased by Glen Jackson, who kicked two goals to punish offside and a collapsed scrum, but whenever the Ospreys moved the ball wide, they threatened.

The longer the game went on, however, the less width the Welsh side offered. They became caught up in a muscular contest in which Saracens conceded nothing, while Kris Chesney and Ben Skirving were invaluable against the Ospreys' international lineout. That played into Hill's hands: the flanker operates off one leg these days but, as is often the way with experienced players, the game appeared to come to him.

The Saracens try came from what appeared at first to be a horrid muddle between Jackson and Neil de Kock, the scrum half finally hoicking a clearance from his own 22 that was touched in flight by Lee Byrne. Instantly Powell recognised the opportunity, took the bouncing ball and sent Leonelli galloping past Ryan Jones on a 50-metre run to the line.

Byrne was sent to the sin-bin for knocking down a scoring pass between Jackson and Richard Haughton, the wing, and though the Ospreys finally worked Paul James over for a try, they had taken too long. In addition, Jackson promptly dropped the goal that meant the Welsh side had to score twice more and, in the remaining two minutes, they were never going to do so.

Scorers: Saracens: Try: Leonelli (42min). Conversion: Jackson. Penalty goals: Jackson 3 (10, 16, 59). Dropped goal: Jackson (78). Ospreys: Try: James (75). Conversion: Hook. Penalty goal: Hook (3).

Scoring sequence (Saracens first): 0-3, 3-3, 6-3 (half-time), 13-3, 16-3, 16-10, 19-10.

Saracens: B Russell (rep: F Leonelli, 30; rep: M Rauluni, 68); R Haughton, K Sorrell, A Farrell (rep: A Powell, 32), K Ratuvou; G Jackson, N de Kock; N Lloyd, M Cairns (rep: F Ongaro, 76), J Visagie, H Vyvyan, K Chesney (rep: T Ryder, 76), P Gustard (rep: D Barrell, 53), R Hill, B Skirving.

Ospreys: L Byrne (sin-bin, 58-68); J Vaughton (rep: A Brew, 65), S Parker, G Henson (rep: A Bishop, 58), S Williams; J Hook, J Marshall; D Jones (rep: P James, 53), H Bennett (rep: R Hibbard, 53), A Jones, I Gough (rep: I Evans, 59), A-W Jones, J Thomas (rep: F Tiatia, 48), M Holah, R Jones.

Referee: A Lewis (Ireland).

Attendance:18,214.