Fly-half Glen Jackson amassed 23 points against Northampton as in-form Saracens notched up their seventh win in eight matches with a 38-15 victory.

Jackson, who signed in 2004 from the Bay of Plenty, emerged victorious from his battle with fellow New Zealand number 10 Carlos Spencer as Sarries ran in four unanswered tries.

The first half was scratchy with Kiwi Spencer getting Northampton on the board after only two minutes after Saracens killed the ball from the Saints' kick-off.

Saracens' centre Kevin Sorrell then went close for the home side as he successfully chased a Dan Scarbrough up-and-under but he was unable to take advantage of a Vaughan Going error and was tackled just inches short of the Saints' line.

Sarries number 10 Glen Jackson then levelled the scores with a penalty before the home side went close again - this time powerful right wing Tevita Vaikona was forced into touch by the scrambling Saints' defence.

Spencer put the visitors ahead again in the 11th minute with another penalty against the run of play, before Sarries finally got the try their first half dominance deserved.

The Saints missed their jumper at the line-out, allowing former Ireland international Shane Byrne to feed Jackson, who in turn spread the ball wide to Kameli Ratuvou to race over for a try.

Saracens landed another penalty before the break, but the reliable boot of Spencer kept Northampton in touch with three further penalties to leave the scores at 16-15 at the interval.

The home side seemed to intent to run the ball in the second half, with the impressive Scarbrough earning the men in black an early penalty after a blistering break.

Unfortunately Jackson was unable to add the three points but the Kiwi outside-half made up for his mistake in the 45th minute as he orchestrated some wonderful running rugby from the Saracens back-line.

Jackson spread the ball from right to left and back again, before throwing a dummy just five metres out and racing through a disjointed Northampton defence to score under the sticks.

Sarries number eight Ben Skirving squandered a glorious opportunity to add his side's third try. Having made an incredible 50-yard break, Skirving threw a dreadful pass to the unmarked David Seymour and the chance went begging.

Saracens domination was not fully reflected in the scoreline until the 68th minute when, with Northampton's pack under severe pressure they crumbled one too many times, leaving referee David Pearson little choice but to award a penalty try, which Jackson converted.

The all-important bonus point was wrapped up with just under three minutes to go. Cencus Johnston - the Pacific Island international - stepped off the bench to make his debut and promptly scored from a line-out. Jackson may have missed the conversion but the win lifted Saracens up to fourth in the Premiership table.