Adams sent the shot to 21.03 metres, setting a meeting record and extending her world-best performance for 2012.
Competing in the historic Olympic Stadium in Rome, Adams started modestly with throws of 19.61m, 19.85m and 20.04m, then exploded in the fourth round with 21.03m, just 21 centimetres below her personal best of 21.24m set at last year's world championships in Daegu, Korea.
She followed up with a final round of 20.86m; five of her six throws would have won the competition.
Surprisingly, her Belarusian arch rival Nadzeya Ostapchuk could only manage third place, throwing 19.58m, a metre below her best this year.
Second place went to Lijiao Gong from China on 19.72 metres.
Adams will next compete at the New York leg of the Diamond League on June 9.
Result: 1. Valerie Adams (New Zealand) 21.03, 2. Lijiao Gong (China) 19.72, 3. Nadzeya Ostapchuk (Belarus) 19.58
