Ned Eckersley hit a third consecutive century for Leicestershire as the Foxes took total control of their County Championship Division Two clash at Wantage Road.
After first day centuries for Marks Cosgrove and Pettini, Eckersley followed his two centuries against Derbyshire with 107, Ben Raine adding 64 in a ninth wicket stand of 140 as the visitors were bowled out for 519. Ben Sanderson easily the pick of the bowlers with 4-58.
Northants then lost two early wickets but Rob Newton and Rob Keogh hit half centuries, the former unbeaten on 66 as the hosts reached 142-4, still 377 runs adrift.
Whilst the first day had been all about Cosgrove and Pettini, the pair leading Leicestershire to 332-5 overnight, Eckersley took centre stage on the second morning resuming on 15 and going on to reach three figures before becoming the last man to fall midway through the afternoon.
Sanderson claimed a career best 7-22 in Northants win at Glamorgan last week, and followed that up in perfect style, after three wickets on the opening day: he removed Pettini, who had added six to his overnight 109, in the sixth over of the day.
Two overs later Clint McKay edged a catch behind to give Sanderson a third five wicket haul of the season, which became six four balls later as Rob Sayer was bowled off his inside edge, trying to leave one.
Three wickets for eight runs had left Leicestershire 356-8, but any hopes the hosts had of dismissing them for under 400 soon went as Eckersley and Raine combined in a record ninth wicket partnership of 140.
With Sanderson removed, the pair were largely untroubled for the rest of the morning and the first part of the afternoon, both reaching a half century in 92 balls, it was something of a surprise when Raine was dismissed, eight short of his career best, edging Keogh to slip.
Eckersley continued however, reaching three figures in the company of last man Charlie Shreck, becoming only the third Leicestershire batsman to score a hundred in three consecutive Championship innings, before holing out soon after.
With 519 on the board, Northants were soon up against it as David Murphy chipped McKay straight to cover in the fifth over and it was 32-2 when captain Alex Wakely edged Sayers’ third delivery behind.
However Newton and Keogh arrested any hopes of a collapse with a composed partnership of 91 in almost 30 overs, on a pitch that, as with so many four day surfaces at Wantage Road this season, was offering little in the way of assistance.
The main danger came from their own running, both batsmen surviving close shaves with throws missing the stumps, Newton reaching his half century with his eighth boundary, before Keogh followed soon after.
Keogh couldn’t add to his score as Neil Dexter provided the breakthrough, Keogh dragging a wide delivery onto his stumps, with six overs remaining Azharullah was sent out as nightwatchman, but he couldn’t reach the close, turning Sayer into the hands of short leg in the final over of the day.