Nick Willis has broken his own New Zealand 1500m record by 0.25s, setting a time of 3m 29.66s to finish fifth at the Monaco Diamond League event.

He earned US$2500 ($3831) for the feat.

Current world and former Olympic champion Asbel Kiprop won the race, using a couple of pace-setters to record 3m 26.69s, the third fastest time in history.

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 couldn't have asked for a better race to run that sort of time. I slotted in near the back and ran dead even splits. I was still a bit disappointed to get behind a second wall of Kenyans behind Kiprop with 200m to go. 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 those guys.

"It's my best race time-wise so I must be in some of the best shape of my life. The blessing of this race on calendar for the world championships versus the London Olympics is that there are six weeks to go rather than three. I will go back to basics and rebuild at altitude from tomorrow.

"This will also give me a good seeding going into world championships [starting August 22 in Beijing], 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 turned 32 on Anzac Day but has excelled over the last 13 months, securing personal bests in the mile (indoors and outdoors), 3000m and 5000m. This is the fourth time he had broken his 1500m mark at the Stade Louis II venue.

He stays away from the athlete hotel by taking an apartment with Team Willis, including wife Sierra and two-year-old son Lachlan, less than a finishing straight sprint on the French side of the Monaco border.

Willis warms up on a jetty leading to a phalanx of multi-million dollar launches, before strolling up the street into the stadium. As he rationalises it: "The All Blacks wouldn't prepare in the same locker room as their opposition". His record at the venue verifies the method.

"I've enjoyed a long bout of health without injuries, which has allowed me to put in an Arthur Lydiard-type mileage base this season," Willis says. "A couple of days ago I ran my best 800m time trial of 1m 46.98s which gives me confidence for the world championships. I want to get it to 1m 44s to have a chance in the last lap of the 1500m final."

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 continued to embed himself in the international shot put ranks with a throw of 20.73m to finish fourth.

New Zealand's top male field athlete, in his first full season as a professional, has embraced his opportunities.

His latest result, in a humid 28 degrees on the Mediterranean, earned US$3000 ($4600)

He was third after the opening round with 20.34m, slipped briefly to fifth in the second round with 20.62m, but regained fourth with 20.73m on his third attempt.

American Ryan Whiting threw 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 in Diamond League appearances 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 some heavy lifting modules, but wanted to throw around 21m today.

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 personal best and meet record of 22.56m. He was 1.32m ahead of compatriot Christian Cantwell while fellow American Reese Hoffa was third with 21.08m.