Wellingtonian Gareth Kean was well below his best in his 200m backstroke heat today, managing just 2min 00.34s, more than three seconds outside his national record.
Keans time placed him 29th among the backstrokers, with the top 16 to move on to the semi-finals.
The fastest qualifiers were Americans Tyler Clary (1min 56.24s) and Ryan Lochte (1min 56.36s).
Kean won a silver medal in the 200m backstroke at the 2010 Delhi Commonwealth Games.
Meanwhile the New Zealand womens 4 x 200m freestyle relay team failed to reach the final.
Weakened by the decision of Lauren Boyle to save herself for the 800m freestyle event tomorrow, the New Zealand quartet finished 11th of the 16 entries.
Their time was 7min 55.92s, nearly 1 outside the time they needed to qualify.
Tash Hind led off for the New Zealanders and turned in a time of 1min 58.79s. She was followed by Samantha Lucie-Smith, Amaka Gessler and Melissa Ingram, none of whom could make an impression on race leaders the United States and Italy.
