With half a kilometre to go, Willis found himself about 50 metres behind Chelanga and Aaron Braun but fought back for a seemingly improbable victory.
Willis had recently won in New York, with victory in the Fifth Avenue Mile in September.
"It means a lot to come back after the Fifth Avenue Mile," Willis said.
Also in Willis' wake were a group of well performed Americans including David Torrence, Lopez Lomong, Ben True and Chris Derrick, Chris Solinsky and Evan Jager.
The day after his race, Willis help out an Italian friend by pacing him in the New York Marathon to the 25km mark, going through the half marathon mark in 1:13.
Meanwhile Lucy Van Dalen won a 5km road race against high quality competition on the Sunshine Coast in Australia on Saturday. Racing in the Asics Bolt 5km.
Van Dalen won in 16:01 ahead of Dutch runner Susan Kuijken who finished 8th in the 5000m at the recent Moscow world championships and Australian Jessica Trengove who was 11th in the Moscow champs marathon. Fourth was Australian world champs 1500m finalist Zoe Buckman.
The Melbourne based former Wanganui runner's win indicates she is well over her achilles tendon injury problems which forced her out of the Moscow World champs and ready for some quick times over 1500m and 5000m on the track this summer.
In the men's Noosa 5km race, New Zealand Cross Country and Road champions Malcolm Hicks from Auckland finished third, again in a top field. Hicks time was 14:12.
The results of Willis, Van Dalen and Hicks on the roads auger well for the New Zealand team Chiba Ekiden Relay in Japan in three weeks.
Willis and Van Dalen will be joined by Holly Van Dalen (Lucy's twin sister), another set of twins in Jake and Zane Robertson and Nikki McFadzien in the six-strong team for the marathon-distance relay.
