Andy Farrell struggled to make an impact on his full debut for Saracens as London Irish opened their EDF Energy Cup campaign with victory at the Madejski Stadium.

The Exiles secured a bonus point with two opportunist tries from scrum-half Richard Rees and scores from Juan Leguizamon, Michael Horak and Riki Flutey.

Fly-half Glenn Jackson was a constant threat for Saracens and it was his angled break midway through the second half that created the opening for Kameli Ratuvou to score.

The Saracens pack heaped the pressure on Irish to earn a penalty try but their comeback stalled when prop Ben Broster was sin-binned with 15 minutes remaining.

Farrell was starting his first senior game 19 months after originally signing for Saracens and with just two reserve games and 15 minutes of first team action under his belt.

The former Great Britain international was again used at blind-side flanker - a position critics feel is a waste of Farrell's natural skills - and never really got into the game.

Farrell spent much of his time in the back line but hardly enjoyed any possession and took 15 minutes to make his first tackle, by which time Saracens trailed 5-3 after Rees jinked through Paul Gustard's tackle to score a sniping try from the back of the scrum.

The heavens opened above the Madejski Stadium and for a period the game was scrappy and riddled with handling errors as the rain teemed down.

Jackson booted Saracens back into the lead after Irish were caught offside and Delon Armitage was then penalised for a high tackle on Ratuvou.

But no sooner had the rain cleared up than the home side drew level. Farrell missed a tackle early in the move and Horak beat Dan Scarbrough down the left wing to score in the corner.

Irish then snatched the half-time lead as number eight Leguizamon broke from the back of the scrum and beat Saracens scrum-half Moses Rauluni to touch down.

It took London Irish just 40 seconds to extended their 19-12 lead after the interval. Rees charged down Jackson's clearance and fell on the loose ball for his second try to wrap up the bonus point.

Delon Armitage then raced through the gears as he hunted down a hack forward from Flutey. He closed in on Jackson and got the touch just before the try line.

Jackson hauled Armitage down off the ball but Flutey had continued his run in support and scored next to the posts.

Jackson's midfield break, helped by Farrell's decoy run, and perfectly delayed pass to Ratuvou earned Saracens their first try of the afternoon.

And things began to get interesting again after referee Bruce Robertson judged London Irish had collapsed a five-metre scrum and awarded Saracens the penalty try.

But Broster was given his marching orders with 15 minutes remaining for a cynical body check on Armitage and with the Welshman went any hopes of a Saracens comeback.

Farrell's rugby union education continues apace and he is due to link up with the England elite squad at their Loughborough University training camp next week.