All of a sudden, Valerie Adams' grasp on a second Olympic gold is looking shaky.

In the space of a month, Adams' main rival, Nadzeya Ostapchuk has beaten the Kiwi's best throw of the year not once, but four times.

Add to that, she has also topped Adams' career personal best twice.

In Minsk on June 12, Ostapchuk has threw a 2012 best of 21.13m, 4cm better than her personal best recorded seven years ago and bettered the Adams' mark of 21.03m she threw at the Rome Diamond League event.

And on Friday last week, the Belarusian smashed that record again, recording three throws over 21m at the Belarus National Championships.

She threw a 21.05, 21.32 and a massive 21.39 to win the event. Her two biggest throws were both significantly bigger than Adams' personal best of 21.24m.

In contrast, Adams' maintained her unbeaten record this season but in not nearly as dominating fashion, with a winning put of 20.97m in a meeting in Tomblaine, France over the weekend.

Adams produced a consistent series of attempts all over 20 metres, but with her rival consistently topping 21m the defending champion will have to be at her absolute best come London.

The Aucklander threw 20.41, 20.62, 20.26, 20.29, 20.97 and 20.54m. Jessica Cerival of France, the 2009 Mediterranean Games champion, was a distant second with 16.67m.

Adams' last competition before the Olympic Games will be in Lucerne, Switzerland, on July 17.

Meanwhile, Kiwis shooting for last-ditch Games spots have come up short in their tilts at qualifying.

In Heusden, Belgium, Zane Robertson, making a last effort to run 3m 35.50s to qualify for London in the 1500m,  was seventh in 3m 38.58s.. Hamish Carson ran 3m 42.84 in the same race.

Robertson's twin brother Jake recorded 13m 26.66s for 14th in the 5000m, outside the 13m 20.00s he required for Olympic qualification.

Monique Williams, in her last attempt to find the form that took her to the 2009 world champs 200m semifinals, came up short in Bottrop, Germany, recording 24.17s, well short of the required 23.00s.

Tom Walsh, also competing in Bottrop, was a metre down on his recent best with a throw of 18.30 metres in the shot put, two metres shy of the required 20.30 metres for Olympic qualification.

There was, though, somewhat of a breakthrough by Angie Smit in Belgium with a massive personal best 800m in finishing second to Beijing Olympic gold medallist Pamela Jelimo of Kenya.

Smit, from Rangiora, North Canterbury, sliced over three seconds off her previous best, set two years ago in Canada, in clocking 2m 00.67s, tantalising close to the New Zealand Olympic qualifying time of 2:00 flat. Jelimo recorded 1m 56.76s.

Smit won the national 800m title at Waitakere in March and was second in the 400m and 1500m. She is now ranked third on the New Zealand all-time list behind Toni Hodgkinson and Nikki Hamblin.

2008 Olympic silver medalist Nick Willis showed good form leading into the Games with a third over 800m in 1m 46.18s, close to his best of 1m 45.54s.

- © Fairfax NZ News