Seamer Matt Henry delivered a quickfire double strike Tuesday to tighten New Zealand’s grip on the first Test against a second-string South Africa.Henry removed David Bedingham and Ruan de Swardt in the sixth over of the day before Clyde Fortuin departed on the stroke of lunch as the Proteas limped to 129-7 on day three in Mount Maunganui.The Proteas trail New Zealand’s 511 by 382 runs, with Keegan Petersen at the crease on 33, having been joined by Duanne Olivier, who is yet to score.Petersen, who has 12 caps, is the most experienced batsman in a depleted South African squad after most first-choice players remained at home to compete in the domestic Twenty20 competition.It has a side with six debutants with a monumental challenge and though Petersen, who was at the crease on two when South Africa resumed at 80-4, advanced resolutely he lacked support.Bedingham departed for 32, having added three to his overnight score before when he skewed an attempted hook off Henry, who has taken 3-31 so far.All-rounder de Swardt impressed with the ball on Test debut but was trapped lbw second ball without playing a shot.Petersen and Fortuin put on 37 for the seventh wicket before the wicketkeeper was caught By Tim Southee at short cover for nine as he attempted to drive spinner Mitchell Santner.