Opener Pettini confidently worked his way to 111 from 111 balls, with Tom Westley (62) and Ryan ten Doeschate (50 not out) also making telling contributions in a total of 269 for four from 40 overs.
Needing more than a run a ball, the hosts were always up against it after losing Vikram Solanki (seven) with the score on 22. Moeen Ali (42) and Phil Hughes (68) went on the offensive but, with wickets falling at regular intervals, they came up short on 244 for eight as Graham Napier took three for 57.
A half-century for Gareth Rees and an all-round contribution from Jim Allenby helped Glamorgan to a comfortable eight-wicket Group B victory over the Scottish Saltires at the Swalec Stadium.
Scotland, who won the toss and elected to bat, were restricted to 151 for nine in their 40 overs with Allenby taking three for 16.
Glamorgan then reached their target of 152 without too many scares and with 12 overs to spare as Rees struck an unbeaten 60 with Allenby alongside him on 39.
Northamptonshire moved off the bottom of Group C with a comprehensive eight-wicket win over the Unicorns at Wormsley.
Having restricted the home side to 163 for eight from their 34 overs, the game having been delayed by the weather, the visitors wasted little time in marching to victory with 46 balls to spare as captain Alex Wakely top scored with an unbeaten 52.
In the county championship, Warwickshire's seam attack put the squeeze on Surrey as the LV= County Championship Division One leaders enforced the follow-on on day three at Edgbaston.
Rikki Clarke led the way with four for 46 while Chris Woakes and Keith Barker shared five scalps with Surrey dismissed for 286, having resumed the day on 109 for one.
Rory Burns top-scored with 77 at the top of the order and although there was some lower order resistance from Stuart Meaker (41) and Jon Lewis (33 not out), Surrey have it all to do if they are to avoid defeat tomorrow.
After being asked to bat again, still 285 runs adrift of Warwickshire, Burns and fellow opener Zafar Ansari negotiated the final 18 overs of the day to close on 38 without loss and give the visitors some hope.
Victory in Birmingham could give Warwickshire some vital breathing room with title rivals Nottinghamshire's bowlers struggling to make any sort of breakthrough against Sussex at Trent Bridge.
Chris Read's men, just one point behind Warwickshire before the latest round of fixtures, looked to be cruising when James Taylor's unbeaten 163 helped them declare on 520 for four - a first-innings lead of 349.
But Sussex's openers put on an unbroken stand of 146, with Ed Joyce making an unbeaten 63 and Chris Nash on 79 not out - on a day where 26 overs were lost to rain to frustrate Nottinghamshire heading into the final day.
At the other end of the table, rock-bottom Durham sealed their first victory of the season by 15 runs over Middlesex in a low-scoring thriller at Chester-le-Street.
Chasing a target of 118, Middlesex resumed on 58 for five and their hopes of triumphing were boosted by nightwatchman Toby Roland-Jones steadily accumulating.
His dismissal for 34 after being caught behind off Graham Onions sparked a collapse as Middlesex lost their last three wickets for four runs in the space of 28 balls.
Both matches in Division Two suffered due to the rain but Adam Lyth's magnificent unbeaten double century lit up Yorkshire's hopes of victory against bottom side Leicestershire at Grace Road.
The promotion hopefuls were all out for 486, with Adam Lyth's 248 not out, his highest first-class score by more than 100 runs, wowing the crowd before Leicestershire slipped to 57 for two - needing another 109 runs just to make the White Rose bat again.
Only 34.4 overs of action were possible at the Ageas Bowl, where Kent advanced their first-innings lead against Hampshire.
Darren Stevens struck 40 as Kent increased their score to 438 for eight and an overall lead of 146 heading into tomorrow's final day.