Karun Nair's majestic unbeaten double hundred put Northamptonshire in a strong position to win their Vitality County Championship Division Two clash with Glamorgan.
The former India Test player hit 202 not out from 253 balls to help his side post a commanding 605 for 6 at Wantage Road, a first-innings total of 334. Nair shared a brisk sixth-wicket partnership of 212 with Saif Zaib, who scored his first ton of the season, as the pair plundered Glamorgan's bowling in support of Ricardo Vasconcelos' knock of 182.
The visitors struggled to 104 for 3 at stumps, still 230 all out, but could be rescued by Monday's forecast of persistent showers. Having lost only two wickets in more than two sessions of batting the previous day, Northamptonshire's progress was soon slowed by a series of three dismissals.
Vasconcelos, who resumed on 166 with the chance of a maiden first-class double hundred in his sights, missed out when Mir Hamza moved a ball just enough to have him caught behind. Brad Wheal looked shaky at first but settled into his rhythm and was rewarded when he edged back to George Bartlett, who was caught at the slips off a leading edge.
Glamorgan promptly replaced Wheal with James Harris - a move that paid immediate dividends as the seamer's second delivery trapped James Sales's leg before leaving the home side five down for 82.
But Zaib's arrival gave the innings a new lease of life as he smashed Harris to the point boundary and edged Zain ul Hassan for four as Nair, who started the day on 55, marched steadily towards his hundred.
The 32-year-old reached three figures when he edged Harris to long leg for two and then savaged Mason Crane, hitting the leg-spinner for successive fours and lifting him over the midwicket fence.
Zaib, who cut and swept with ruthless precision, was dropped on 71 by Crane's reverse-sweep to Ul Hassan at backward point and began to get bogged down in the 90s.
Needing one for his century, Zaib was given another life when Colin Ingram dropped him at gully off Dan Douthwaite - and the left-hander took advantage, scooping a single before holed out to deep square leg in Crane's next over for exactly 100.
Nair continued to punish a subdued Glamorgan attack, hitting Wheal for a single to pass 200 for the third time in his career and triggering an immediate declaration from home skipper Luke Procter.
That left Northamptonshire with 40 overs to bat, and the visitors' opening pair 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 had the desired effect.
Spinner Zaib, moving 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 in the slips.
Glamorgan's prospects almost deteriorated immediately when Ingram edged to Nair at first slip, but he and Kiran Carlson saw their side through to the close.