He had to work hard to stay alive in the race, being one of the victims of some unforgiving running which had Kenyan Ronald Kwemoi, the fastest qualifier into the final and world No 1 rated athlete, tumble to the track.
For Willis, 33, it completes a fine meet. His semifinal run suggested not only was he running well, but he was racing strongly, an important distinction.
"I proved to myself I still had it in me. You're never quite sure, especially when you start getting greys in your hair," Willis quipped.
"I stayed away from social media for a month. I wanted to get away from any distractions. It wasn't the goal but it's still very nice to get up on the podium."
Willis has carried on a fine New Zealand 1500m tradition today.
It started with Jack Lovelock's legendary gold at Berlin in 1936 and continued with Peter Snell (gold) and John Davies (bronze) in Tokyo in 1964.
John Walker picked up the baton in 1976 at Montreal with his gold medal and Willis won silver - having been promoted after crossing in third place - in Beijing in 2008.
Now he's the first New Zealander to have won two 1500m Olympic medals.
''It got very slow and I really wasn't all that confident in the warmup, right before the start line. I was like 'come on, get your head in it! It's the Olympic final, do you really believe you can win?'.
"I thought maybe I could sneak home for a bronze from the back, but when it slowed down it gave me a chance to get in the game."
The big point his support team and family were drilling into him was keep wide, to get a clean run.
"But when I got to 450m to go the only guys in front of me were the favourites so I knew they were guys that could hold it all the way to the home straight. Then it would pan out and thankfully it did. I gambled by trusting in the ability of those guys but they brought me home."
Willis acknowledged at times he thinks too much about his racing. He said he contacted the great British runner Steve Ovett two years ago and asked if he could skype with him to "get my head back in it".
"He said 'you think too much Willis! Stop thinking and just race you bugger'. So I think that's helped out."
Willis' success is New Zealand's fifth bronze of the Rio Games, and the fourth medal on the athletic programme, after shot putters Val Adams (silver) and Tom Walsh (bronze) and Eliza McCartney's bronze in the pole vault yesterday.
