Anstiss (18) retained the Ken Reddington trophy for the lowest score of the day, adding a 70 to his morning round to finish eight under for the day.
His 66 follows an Alexandra record of 65 when he birdied the final six holes to win the Central Otago championship last weekend.
In what has been a great year for setting course records so far,
Jason Hughes scored a 67 at Port Chalmers while Brandon Hodgson posted a 68 at Otakau.
But the daddy of them all was a scintillating 59 by Inian Logan (15) in the intercollegiate tournament at Roxburgh three weeks ago.
Anstiss made three birdies on the outward nine and four coming home. His only blemish was a bogey 4 on the par 3 17th.
He finished 11 shots ahead of his nearest rival, with Scott Hansen (Southland) winning the under-23 section on 147.
Conor Jamison (Chisholm Park) and Sungwoo Han (Queenstown) also finished tied on 147 for second place in the under-19 event.
Inian Logan scored 79 and 73 to win the under-16 section by six shots from Queenstown's Jack Turner, with Connor Ross (St Clair) one further stroke back.
Callum Judkins shot 80 and 77 to take the under-14 boys, while once again Laura Hoskin (Arrowtown) was the leading girl.
Hoskin scored an 81 in the morning but made five birdies in the afternoon on her way to an impressive 73.
Abigael Crawford (St Clair) came in second with rounds of 87 and 81.
