Winner previously in 2007 and 2013, Coster shore the dozen coarsewools in 18min 33.63 sec, Kirkpatrick finishing next in 19min 39.27sec.
The time-points advantage, along with second-best combined board and pen points, was something no one else was able to overcome, and Coster eventually claimed the win by a comfortable margin of almost five points from defending champion Nathan Stratford, of Invercargill.
Kirkpatrick had to settle for third, and fourth was Mataura shearer Brett Roberts, who had the best combined points on the board and in the pens.
Cutting back on the competitions hasn't meant cutting back on the shearing for Coster, who with his wife also runs a courier van. He said he'd just come off the lambshear, and his fitness was "pretty good."
"It's that you just don't really have quite that confidence against the guys that are shearing competitions all the time," he said, with world teams champions Stratford and Kirkpatrick having been in action on a weekly basis since the season started at the beginning of last month.
Coster's "retirement" simply means retreating from the same schedule, and he didn't enter the PGG Wrightson Wool National Circuit, the first time absent in more than 20 years of Open competition in which he won the series four times.
"I think since even before PGG Wrightson became the sponsors," he said, reflecting on his years in the series which ends with a final each year at the Golden Shears and which originated with the first presentation of the McSkimming Memorial Triple Crown in 1973.
"They've been very loyal sponsors," he said, with PGG Wrightson in their 17th year with the event.
Series leader Tory Pyper, of Winton, was unable to be at today's show, but had already guaranteed a top-12 place for the March showdown after strong performances in heats at Alexandra (finewool) and Waimate (strongwool).
Top series and also probable finals-qualifying points today went to Ringakaha Paewai, of Gore, and Ethan Pankhurst, of Masterton, who were first and second in the heats, which had 24 shearers chasing the Canterbury title, among the 74 entries across the five classes, with 33 woolhandlers having competedon the first day of the annual championships.
There was a significant upset in the Blade shearing final with 2010 New Zealand World Championships representative Allen Gemmell, of North Canterbury, ending the run of Fairlie farmer Tony Dobbs, who had been unbeaten in the event since coming out of retirement from competition in 2013. Gemmell had won once previously, 17 years ago.
South Island-based Chilean World Championships representative Luis Pincol had his biggest win, after a string of minor-show triumphs, by winning the Senior final by more than six points from runner-up and well-performed Taumarunui shearer Lionel Taumata, who was first to finish in a tick over 14 minutes for 6 sheep.
Marlborough shearer Duncan Higgins won the Intermediate final and emulated the achievement of sister Sarah who won the Intermediate final last year. It was, however, a close call with Higgins' fastest time of 10min 47.93sec for four sheep, more than two minutes quicker than second-fastest Kelly Macdonald, of Lake Hawea, being crucial to holding-out Winton's Brandon Maguire Ratima, who had easily the best quality points in pen judging and missed the major prize by just 0.2pts.
The Junior final was won by Mitchell Menzies, of Ranfurly, by a wide margin of more than 11pts from runner-up Darcy Tong, from Timaru.
Results from the Canterbury A and P Show's New Zealand Corriedale Shearing Championships at Christchurch on Friday, November 17, 2017:
Open final (12 sheep): Tony Coster (Rakaia) 18min 33.63sec, 78.682pts, 1; Nathan Stratford (Invercargill) 19min 56.19sec, 83.56pts, 2; John Kirkpatrick (Napier) 19min 39.27sec, 84.13pts, 3; Brett Roberts (Mataura) 21min 30.53sec, 86.943pts, 4; Paerata Abraham (Masterton) 19min 45.18sec, 99.509pts, 5; Ringakaha Paewai (Gore) 22min 24.91sec, 100.496pts, 6.
Senior final (6 sheep): Luis Pincol (Chile) 14min 51.16sec, 71.725pts, 1; Lionel Taumata (Taumarunui) 14min 0.97sec, 77.382pts, 2; Linton Palmer (Dipton) 14min 38.32sec, 81.749pts, 3; Corey White (Waimate) 14min 5.25sec, 84.263pts, 4; Mitchell Murray (Amberley) 15min 53.31sec, 88.166pts, 5; Jarrad Morgan (Makakihi) 17min 47.06sec, 89.52pts, 6.
Intermediate final (4 sheep): Duncan Higgins (Havelock) 10min 47.93sec, 68.897pts, 1; Brandon Maguire Ratima (Winton) 13min 234.94sec, 69.197pts, 2; Duncan Leslie (Owaka) 71.499pts, 3; Sam Thomson (Waipara) 14min 42.21sec, 80.611pts, 4; Kelly Macdonald (Lake Hawea) 12min 56.29sec, 97.315pts, 5; Allan Oldfield (Geraldine) 14min 8.38sec, 107.919pts, 6.
Junior final (3 sheep): Mitchell Menzies (Ranfurly) 12min 53.49sec, 76.675pts, 1; Darcy Tong (Timaru) 16min 21.03sec, 88.052pts, 2; Will Haakma (Tapawera) 11min 45.8sec, 90.623pts, 3; Jonah Karena Tutapu (Mataura) 10min 42.56sec, 95.795pts, 4; Fred Kighton (England) 15min 44.63sec, 100.232pts, 5; Cody Davidson (Hakatere) 13min 36.47sec, 111.157pts, 6.
Blade shearing final (5 sheep): Allan Gemmell (Rangiora) 17min 6.37sec, 70.719pts, 1; Tony Dobbs (Fairlie) 17min 58.84sec, 74.452pts, 2; Brian Thomson (Christchurch) 18min 40.41sec, 81.621pts, 3; Mike McConnell (Timaru) 19min 30.25sec, 85.913pts, 4; Allan Oldfield (Geraldine) 19min 42.22sec, 89.111pts, 5; Phil Oldfield (Geraldine) 18min 11.63sec, 97.982pts, 6.
