Ben Spencer won the battle of the kickers to secure Saracens back-to-back LV= Cup triumphs with victory over Ospreys in tough conditions at the Gnoll.
The scrum-half scored all the points for the visitors as a youthful Saracens side backed up their 25-20 success over Harlequins last weekend to steal a march on their Pool One rivals.
Ospreys fly-half Sam Davies landed three penalties of his own but his side struggled to cope with the dominance of a Saracens pack marshalled by England Under-20s captain Maro Itoje.
The hosts were routinely penalised at the breakdown and the scrum with prop Gareth Thomas sent to the bin, allowing Spencer to take full advantage with a composed kicking display despite the driving rain.
Although Saracens also had winger George Perkins carded after only 19 minutes, the Aviva Premiership Rugby side remained in control to inflict only a second defeat of the season in all competitions on the Ospreys.
Saracens took the lead after six minutes when recent signing Brett Sharman carried forward well and Ospreys were penalised for not releasing, with Spencer landing his penalty attempt.
Spencer doubled his side’s advantage five minutes later as another Saracens excursion into the Ospreys’ 22 saw the hosts pinged once more and the scrum-half made no mistake from the tee.
With conditions making handling tough, both kickers needed to take their chances and Davies duly got his side on the scoreboard with a successful penalty to make it 3-6.
Ospreys were handed a further boost on 19 minutes when Perkins was sent to the bin for taking out opposing flyer Dafydd Howells in the air.
Davies, the 2013 IRB Junior Player of the Year, slotted the resulting penalty from distance to bring the scores level at 6-6.
The 21-year-old then missed a difficult chance to put his side in front as his attempt from within his own half fell narrowly short.
His kicking counterpart Spencer made it three from three in the 28th minute to restore Saracens’ lead after a mix-up in the Ospreys back field gifted the visitors another penalty.
The home side failed to exploit their man advantage as they were penalised for coming in at the side, allowing Spencer to score his fourth penalty as Perkins returned to the field.
Ospreys immediately rallied to set up a catch and drive metres from the Saracens try line only to knock the ball on as the score remained 6-12 at the break.
The hosts were left to rue that missed opportunity just two minutes into the second period when Thomas was binned for a dangerous tackle, although Spencer offered a slight reprieve by dragging his penalty effort wide.
With the rain finally abating, Ospreys were in the ascendancy as they went back up to 15 men, forcing Saracens to stray offside before Davies bisected the posts to reduce the deficit to three points.
Yet their ill-discipline at the breakdown once again proved costly as Spencer recorded his fifth successful penalty attempt to put his side 15-9 ahead.
The half-back added a sixth on the hour as a powerful drive from the Saracens pack at a scrum forced Ospreys into making another infringement.
Saracens’ forwards continued to exert their dominance with the hosts conceding their third penalty in as many minutes, but Spencer’s long-range attempt fell just under the cross bar.
Ospreys kicked for touch after a penalty deep in Saracens territory inside the last ten minutes but the visiting defence turned the ball over and cleared their lines.
Superb defensive work from Saracens set up another penalty attempt for Spencer in the final few minute, with the scrum-half converting from the tee to make it 21-9 as Saracens controlled the final stages.
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