McEwan made an indifferent start with a 5-over 76 on Saturday morning to lie tied for sixth place, five strokes behind leader Brandon Hodgson (Otago).
Anstiss shared second with Nick Borren (Otago) and Mark Brooks (Queenstown) on 73.
In the afternoon, the winds strengthened and strong blustery gales made low scoring almost impossible.
But McEwan, a refreshed man after his Christmas break, had other ideas after turning 1-under-par.
He shot a tremendous 4-under 31 coming home for a round of 66 which turned his five-stroke deficit into a four-stroke lead overnight.
McEwan thrives in windy conditions but, by his own admission, the second-round climate was more than he wanted.
McEwan posted a par round yesterday morning while Anstiss, with a 2-under-69, closed the gap to two shots.
Hodgson was in third place, 10 shots off the pace, and the final round became a contest between McEwan and Anstiss.
With a 1-under 70, McEwan staved off any challenge. Antiss finished second and Hodgson was third.
Ryan Bellamy (Port Chalmers) easily won the senior B title with a four-round score which tied him for sixth in the overall field.
Fifteen-year-old Terry Kim (Queenstown) took the intermediate title by six shots while Kyle Geary (Chisholm Park) carded 82 in the wind and 74 yesterday to win the masters (over-40) title decided over 36 holes.
Sergio Garcia claimed his first European Tour victory for more than two years yesterday when he beat Finn Mikko Ilonen at the third hole of a playoff at the $US2.5 million ($NZ3 million) Qatar Masters, Reuters reports.
Both players finished the regulation 72 holes on 16-under-par 272, one ahead of Spaniard Rafael Cabrera-Bello (69) and Dane Thorbjorn Olesen (68).
Garcia (65) and Ilonen (66) then carded matching birdie fours at the 18th in the first two holes of the playoff.
The second from the Spaniard came after a magical bunker shot to tap-in range just when it looked as though the title might be heading to Finland.
The pair kept playing the 18th and, at the third time of asking, Ilonen could only manage a par after finding rough off the tee and a bunker with his second shot while Garcia hit the green in two and safely two-putted for yet another four.
The 34-year-old broke into a wide smile before embracing his delighted caddie as Garcia won on the tour for the first time since landing the Andalucia Masters crown in October 2011.
''This feels good,'' Garcia said after following up his Asian Tour triumph at the Thailand Championship last month.
''I started the day thinking that if could shoot 6 or 7-under maybe I would have a chance.''
