Playmaker Glen Jackson inspired Saracens to their fifth Guinness Premiership victory of the season with an inspirational second-half performance.

The New Zealander, who is poised to qualify for England on residency grounds, took just 90 seconds to put Saracens ahead with a drop-kick after replacing Gordon Ross at the interval.

But the fly-half's most telling contribution came three minutes from the hooter when he spurned a penalty in front of the posts and instead kicked across to Richard Haughton and the right wing was alert to gather and touch down.

The lead changed hands six times as Irish, who had won five of their previous six meetings at Vicarage Road, struggled with the boot despite Delon Armitage claiming a 14-point haul which included a first half try.

But the hosts edged it to extend their best start to a league campaign for nine years.

It was not all plain sailing for the hosts and the pack will welcome the arrival of Chris Jack, the New Zealand international who joins this week.

Armitage's eighth-minute touchdown was the best moment of an error-strewn first half.

Hooker David Paice was stopped a metre short on the left wing but the ball was recycled quickly and Peter Richards popped the ball to the outside centre running on a direct line to crash over.

The hosts struggled to breach the visitors' 22 throughout the half but Ross' boot kept them in touch and he pulled three points back with a drop-goal before putting his side ahead with a 40-metre penalty midway through the half.

Seilala Mapusua was fortunate not to visit the sin bin for a cynical late hit on Haughton but Ross later punished the visitors with another long-range penalty.

Armitage replied with a penalty from the halfway line after taking over the kicking duties from Peter Hewat, who missed the earlier conversion and had been dazed by some big hits.

Kris Chesney, making his 301st appearance for the hosts, offered Armitage another three points after pulling off the blindside of a scrum too early, but the centre spurned the straightforward opportunity to put Irish ahead. But he then did so with a 36-metre effort.

Jackson replaced Ross at half-time and immediately put Saracens ahead with a drop goal.

Hewat put the Exiles in front with a penalty after David Seymour had been penalised in the tackle.

But Saracens hit back when Haughton made a scything 30-metre run and was stopped 10 metres short. Quick ball allowed Adam Powell, playing instead of the rested England centre Andy Farrell, to touch down from close range.

Jackson successfully converted to establish a five-point lead, but Hewat reduced the arrears to two with a penalty.

Irish put sustained pressure on the hosts' line with number eight Phil Murphy stopped inches short after peeling off the scrum. But Hewat sliced a drop-goal attempt wide from 15 metres to concede territory.

Another long-range effort from Armitage put the Exiles a point in front with 10 minutes remaining.

But Irish conceded a late penalty in front of the posts and Jackson unexpectedly opted to kick to Haughton who dived over.