Tomorrow, he will make his debut for the Highlanders, taking on the Stormers at Forsyth Barr Stadium.
It has happened very quickly for Lentjes, a St Bede's College old boy, who headed south after completing his studies at the University of Canterbury.
After a successful club season with Taieri, he played for Otago last season and was named rookie of the year.
The 23-year-old trained with the Highlanders before Christmas but did not make the initial 32-man squad or the wider squad.
But he impressed enough to be called in to make up the numbers, and when both Shane Christie and John Hardie went down, Highlanders coach Jamie Joseph called the Taieri man into the squad last week.
Now, he gets the start against a tough Stormers side.
''He is a specialist seven, has been part of our pre-season and knows all our systems.
''He is a player of the future for us,'' Joseph said.
''He gets a good opportunity to play what is against a very physical Stormers side ... it is a good opportunity to give James a start. He is physical and fresh, and does not have a reputation. No-one knows about him.
''His physicality is a stand-out feature for us. He is good at the breakdown and we feel that the South Africans are going to come pretty hard in that area.''
Lentjes, who played pre-season games for the Highlanders, had 50 minutes at openside flanker for Taieri in its big win over Pirates last Saturday.
He will be the fourth openside flanker used by the Highlanders in six games.
Joseph said it was touch and go whether Hardie (ankle) and Christie (hamstring) would go to South Africa in May and they would would not be back for at least five weeks.