In 2004, Carlos Spencer struggled to find the same form he had displayed the previous year, and Mehrtens replaced him for the final game of that year's Tri Nations. He was then ruled out of the final All Black tour of the year through injury. In 2005 Spencer lost form early in the Super 12 competition and then suffered a fractured cheekbone in training. He agreed to play for the New Zealand Māori (in his 10th match for that team) against the touring Lions, but made himself unavailable for the All Blacks so that he would not miss training for his new English club, Northampton Saints.