But at one down on the head, Girvan chose to drive the shot bowl out and so win the game, only to lose all his own bowls and drop a crucial three shots.
Curran quickly added the two he needed for the win.
"I was quite surprised he did that," the eight-times Harbour centre champion said after the match.
There were few other upsets as the singles reached today's closing rounds, though current Harbour singles champion, Peter Nathan of Birkenhead, missed out to Takapuna's John McCormack in the first round of post-section despite a late run, and last year's runner-up, Australian Sean Ingham, also left early.
Two of New Zealand's most decorated bowlers, Gary Lawson and Peter Belliss, reached the last 16, and Auckland's Petar Sain remained on course for a possible double as he has already made the pairs final, with Rob Ashton.
Lawson won one of the day's most pivotal showdowns, against the 2001 national pairs champion, Mike Galloway of Hillsboro, who has returned to serious bowls after concentrating on family commitments and his work as a greenkeeper. But against Lawson, he could not find his old drawing touch and lost 21-11.
Another key clash was that between the former New Zealand Open champion Neil Fisher and fellow Aucklander, former Black Jack Danny Delany.
Fisher won by a surprisingly comfortable 21-11.
Dunedin's Mike Kernaghan, with consecutive national singles titles in 2001-02, was another in ominous form, winning his final match 21-4.
Other multiple national champions, Alvin Gardiner of Canterbury, Lance Tasker (Bay of Plenty) and Mike Solomon (Wellington), are also in today's last 16, with Mike Hall (Otahuhu Railway), Neil Barron (Hawkes Bay), Australian-based Eric Taylor, James Gavin (Ellerslie), David Hood (Kerikeri), Cameron Nairne (Taranaki) and Adam Wishnoski (New Lynn).
Though he missed the final 16, losing to Taylor, Takapuna's Bevan Smith, a former Olympic and Commonwealth Games track athlete, put up a remarkable effort to go so far in post-section.
Smith is in only his third season playing the game, but among those he beat in section play was the redoubtable Sain.