He never did need that duck.
Although Kenyan Joseph Kiplimo was closing fast in fourth, and although Robertson had just about exhausted his energy reserves, the 24-year-old managed to hang on and write another chapter in this country's fine tradition in the black singlet.
Robertson and twin brother Jake are something of an unknown quantity for Kiwi sports fans, leaving their home in Hamilton to base themselves in Kenya, but that decision certainly reaped rewards today. In addition to Zane's podium place, Jake ran near the front of the field until, cruelly, two laps from the finish when he collided with compatriot Nick Willis, ruining both men's races.
At the time of that incident, New Zealand and Kenya occupied the first six spots at the head of the leading bunch. While Isiah Koech would have been difficult to pip for silver, both brothers knew Jake was in line for a top-five finish.
"I feel so bad that he went down, but I know he feels happy for me and we're probably going to be celebrating tonight," Zane said. "I was [aware he fell] because I heard the crowd and I took a look back just before I took off. I think I was leading at that point but I did see who had gone down.
"I just thought, 'Oh my God, what can I do here?' You just need to focus on what you're doing still because the job is at hand and there's nothing you can do for him."
While the fallen Robertson did recover and battled back to finish ninth - a spot ahead of Willis - it could have been so much better. Battered and bruised, Jake was hopeful of recovering in time for the 10,000 on Saturday morning (NZT) but, if not, he was intending to use the disappointment as motivation for the next Games cycle.
"I've got four years to use this as a positive instead of a negative," he said. "I could go away and cry like a little kid, but I'm just going to go away and use it.
"But I'm really happy for my brother. We planned to work as a team and we were going to get two medals, I think."
Even with just one, the Robertsons earned a slice of history. Today's was the first medal New Zealand have won in the event since the metric conversion of race distances, with Murray Halberg previously winning back-to-back golds in the three-mile (4800m) event.