All Blacks Coach Steve Hansen has called two of his most senior players “dumb“ after their poor discipline hurt the All Blacks in their opening Rugby World Cup win over Argentina this morning.

The World Cup holders were briefly reduced to 13 men after captain Richie McCaw and centre Conrad Smith were both sin‑binned in the first half of the 26‑16 win.

McCaw's came first when he tripped an Argentina player to prevent a quick tap, before Smith infringed at the breakdown with the Pumas hot on attack.

Both were obvious infringements and easy decisions for English referee Wayne Barnes.

Hansen says he was not impressed at having to spend time with more than 200 Tests worth of experience in the sin‑bin.

McCaw himself admitted he made a dumb mistake and couldn't blame fans for being angry with him.

The All Blacks face Namibia at 7am Friday.