Importantly, the result places Willis in contention to become the first New Zealand man to earn a medal in the 32-year existence of the world championships. The next edition starts on August 22 in Beijing.
"It's my best race time-wise, so I must be in some of the best shape of my life," Willis said. "The blessing of this race on the calendar before the world championships versus the London Olympics is there are six weeks to go rather than three. I will go back and rebuild at altitude.
"This will also give me a good seeding going into world championships, so the heats won't be stacked with too many good guys. It puts me in the top five or six in contention for medals."
Willis stayed at the back of the field for the most part and even expressed frustration at not breaking into a better position on the home straight.
"I wasn't sure whether to go to lane three, or wait until the home straight and wait for a gap. It took a long time but I got through. I crossed the line not feeling the jubilation I thought after running a sub-3m 30s. I really wanted to finish in the top two. I was ready to drive more, but it's my fault for being slightly behind."
Willis turned 32 on Anzac Day but has excelled in the past 13 months, securing personal bests in the mile (indoors and outdoors), 3000m and 5000m.
He stayed away from the official athlete hotel by taking an apartment with Team Willis, including wife Sierra and son Lachlan, 2, less than a finishing straight sprint from the stadium on the French side of the Monaco border.
Willis warmed up on a jetty leading to a phalanx of multi-million-dollar launches, before strolling up the street into the stadium. As he says: "The All Blacks wouldn't prepare in the same locker room as their opposition." His record at the venue verifies the method.
Willis has raced in Europe since 2001, but his body can still foot it with youth.
"I'm surprised to be feeling so energetic in my legs, which indicates I might be able to keep handling the rigours of training.
"I think the statistics around age are skewed by an amateur era when people did sport until it was time to get a real job. Professionalism means people can dedicate themselves longer."
Fellow Kiwi Tom Walsh embedded himself further in the shot put ranks by finishing fourth with a third-round effort of 20.73m.
As New Zealand's top male field athlete, in his first full season as a professional, he earned US$3000 ($4600).
American Ryan Whiting recorded the same mark but finished below Walsh because the New Zealander had the next best measurement of 20.69m with his fourth throw.
Walsh has consistently delivered in excess of 20.70m this season (20.81m for fourth at Eugene, 21.16m for third at New York and 20.86m for fifth at Lausanne).
He says the fourth and fifth placings came after heavy lifting modules, but he wanted to throw around 21m yesterday.
His aim is to reach a personal best of around 21.50m at the world championships.
His current mark, 21.37m, was set in March at Melbourne.
American Joe Kovacs won with a PB and meet record of 22.56m. The throw was eighth on the all-time list. He was 1.32m ahead of compatriot Christian Cantwell. Fellow American Reese Hoffa was third with 21.08m.
