O'Connor, from Queenstown, has 18 centre titles, while O'Callaghan, from Alexandra, has 28. Buchanan, who is O'Connor's regular club lead, has only played the game since 2008 and has already picked up seven centre titles.
Another Aucklander, Neil Fisher, like de Jongh, also had the chance of winning two titles, following his win in the triples on Thursday. But he, too, missed out, losing the men's singles final to Waikato's Tony Fabling 21-15.
Fabling, a one-time A grade squash player who 10 years ago gave up that sport at 40 only because it became too hard on his body, always held command over Fisher, jumping away to an 8-2 lead which he never surrendered.
His effort took him one step ahead of his uncle George, another who turned to bowls after reaching a high level at squash.
In 1987 George was a beaten finalist in the national pairs championship.