Smith who won the half marathon of the same event in 2008, clocked two hours, 18 minutes, 14 seconds for the 42.2km run.
The race was contested in less than ideal conditions with light rain and temperatures of 11degC making a for a tough day.
Christchurch's Luke Hurring outsprinted Ethiopian Wondwosen Geleta for second place seven minutes behind Smith.
The women's event was won by Australian Magda Karimali-Poulos who led from start to finish to be a comfortable winner in 2hrs 46min 32secs.
Sara Biss was second in 2hrs 53min 29secs, while Wellington veteran Suzi Richards claimed third in 2hrs 55min 07secs.
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