Northamptonshire 605 for 6 dec (Nair 202*, Vasconcelos 182, Zaib 100*) lead Glamorgan 271 (Ingram 82, Crane 61, Sanderson 5-92) and 104 for 3 (Root 41, Sanderson 1-22, Zaib 1-22) by 230 runs

Karun Nair's majestic unbeaten double hundred propelled Northamptonshire into a strong position to push for victory in their Vitality County Championship Division Two battle against Glamorgan.

The former India Test player racked up 202 not out from 253 balls to underpin his side's commanding total of 605 for 6 declared at Wantage Road, a first-innings advantage of 334. Nair shared a brisk sixth-wicket partnership of 212 with Saif Zaib, who registered his first ton of the season as the pair plundered Glamorgan's bowling to back up Ricardo Vasconcelos' knock of 182.

The visitors laboured to 104 for 3 at stumps, still trailing by 230, although they could be rescued by Monday's weather forecast for persistent showers. Having lost only two wickets during more than two sessions of batting on the previous day, Northamptonshire's progress was soon slowed by a cluster of three dismissals.

Vasconcelos, who resumed on 166 with the opportunity of a maiden first-class double hundred firmly in his sights, missed out as Mir Hamza moved a ball away just enough to have him caught behind. Brad Wheal looked wayward initially but settled into his rhythm and gained some reward when he brought one back at George Bartlett, who was taken in the slips off a leading edge.

Glamorgan promptly replaced Wheal with James Harris - a move that paid off immediately as the seamer's second delivery trapped James Sales leg before to leave the home side five down and just 82 ahead.

However, Zaib's arrival brought the innings renewed impetus as he thumped Harris to the point boundary and cut Zain ul Hassan for four more, while Nair - having begun the day on 55 - advanced steadily towards his hundred.

The 32-year-old reached three figures by turning Harris to long leg for two and went on to savage Mason Crane, thumping the leg-spinner for successive fours and lifting him over the fence at midwicket.

Having cut and swept with ruthless precision, Zaib was dropped on 71 reverse-sweeping Crane towards Ul Hassan at backward point and gradually became bogged down during the 90s.

With one needed for his century, Zaib was handed another life when Colin Ingram spilled him at gully off Dan Douthwaite - and the left-hander took advantage by shovelling a single before he holed out to deep square leg for exactly 100 in Crane's next over.

Nair continued to punish a subdued Glamorgan attack, pushing Wheal for a single to pass 200 for the third time in his career and triggering an immediate declaration by home skipper Luke Procter.

That left Northamptonshire with 40 overs to make inroads, but the visitors' opening pair initially looked comfortable as Billy Root steered both Ben Sanderson and Chris Tremain to the cover fence.

They put on 46 before Northamptonshire's teenage seamer Raphy Weatherall made the breakthrough, persuading Ul Hassan to flash outside off stump - and Procter's bowling changes then produced the desired effect.

Spinner Zaib, switching to the David Capel End, turned one out of the rough to fox Root for 41 and Sam Northeast fell to Sanderson in the next over, courtesy of Emilio Gay's juggling act in the slips.

Glamorgan's prospects almost worsened immediately as Ingram edged to Nair, who put it down at first slip, but he and Kiran Carlson saw their side through to close of play.