The former All Blacks fly-half kicked five penalties and converted tries by James Johnston and England winger Ugo Monye.
Irish responded with two excellent tries from former England winger Topsy Ojo, with full-back Tom Homer kicking four penalties and a conversion.
Saracens' return to Twickenham ended on a sour note as they were dealt a 20-15 opening-day defeat by Wasps.
The defending champions, back at the game`s headquarters for the first time since their title win over Leicester in May, allowed Wasps to come from behind and take the win with a late Tom Varndell try.
The defeat continued a curse for any side defending its title, with Saracens becoming the ninth team to suffer an opening-fixture loss in 11 years.
Leicester fly-half George Ford missed two crucial drop-goals as Exeter secured a 30-28 win at Welford Road.
It is almost a year since Exeter let slip an 11-point lead at Leicester as they went down 37-27 - but on Saturday it was a different story.
Exeter scored tries through Sireli Naqelevuki, Tom Johnson and Matt Jess, with Ignacio Mieres kicking 15 points.
Thomas Waldrom and Niall Morris with a brace were the try-scorers for the Tigers. Ford landed one drop-goal, with Billy Twelvetrees contributing the rest of their points.
It was the Sam Vesty show at Kingston Park as the Bath fly-half rattled up 17 points from four penalties, a drop goal and a conversion and engineered the game's only try as his side rumbled to a comfortable 22-9 Premiership victory over Newcastle.
Bath's pack dominated the game and Newcastle did themselves no favours by conceding lots of penalties, mainly at the breakdown, and an early try from Matt Carraro from which they never really recovered.
Three first-half penalties from Jimmy Gopperth was all Newcastle could manage.
Worcester resumed life in the Aviva Premiership with a hard earned 17-12 win over a spirited Sale side at Sixways.
The Warriors scored the only two tries of the game and should have won more comfortably with Sale only having 12 points from the boot of Nick Macleod to show for their efforts.