Valerie Adams says she was not her normal self as her arch-rival Nadzeya Ostapchuk produced a stunning set of throws to take the Olympic women's shot put title.
Adams threw 20.70m, further than she threw to win Olympic gold four years ago in Beijing.
But Ostapchuk threw better than 21.30m three times - a distance Adams has never reached despite her multiple world titles - and the New Zealander says it wasn't her day.
"My aggressiveness wasn't there like it used to be. I left my heart out there trying to find my aggressiveness in me and it just didn't come together," a tearful Adams said after the competition.
"I put my heart out there trying but unfortunately I walked away with silver. It was Ostapchuk's day."
Adams says she's happy to win a medal for New Zealand but disappointed she didn't throw the way she wanted and indicated she wants her title back in four years' time.
"As an athlete you always want more and we trained really hard and training was going good, but it's sport, it's life," she said.
"I might just go to Rio just to piss people off."
Adams held every title in the women's shot put coming into Monday's event, including the Olympic title from Beijing in 2008, and had won 24 consecutive competitions since her last defeat in 2010.
But Ostapchuk had the best throws of the year and it translated into the Olympic Stadium.
Adams was in front with 20.61m after the first throw but a 21.31m second throw from Ostapchuk blew the New Zealander away.
Adams improved to 20.70m with her third throw but Ostapchuk responded with 21.36m, to which Adams could not respond.
Coach Jean-Pierre Egger said Adams was not her usual self.
"If I analyse her dynamics, it was not very dynamic. Why? Because something blocked her. It's very difficult to know what until I have more time to have a discussion with her."
Russia's Evgeniia Kolodko won bronze with a final throw of 20.48m.
Adams was looking to become be the first person to successfully defend the women's shot put title since Tamara Press in 1964.
It was New Zealand's first silver medal of the 2012 Olympics and brings their medal tally to eight.