They had won the match convincingly, but Lomu had again performed poorly and coach Mitchell was unable to pinpoint why.
"An unknown winger had gone around Jonah very easily in the game to score," Mitchell, 51, told me.
"And I can still picture him sitting there in the changing room afterwards, looking bewildered. He was a shadow of his former self and we were at a loss to explain why.
"Afterwards I had to sit down with him and his manager and explain that he was not meeting the performances expected. It was very tough to do that.
"As an All Black, you have to meet incredibly high levels of performance, regardless of your reputation or how much I like you as the coach. And I really did like Jonah."
The reasons for the decline became clearer in 2003, when Lomu was diagnosed with a rare kidney disorder called nephrotic syndrome.
He had a transplant in 2004, but the complaint continued to dog him for the rest of his life, heavily contributing to his death on Tuesday at the age of just 40.
The warning signs had been there during a 2002 training camp in Coromandel, just a short time before that Fiji game.
"Jonah was really struggling with the anaerobic work we were doing," recalls Mitchell, who was All Blacks coach from 2001 to 2003.
"The data was telling us he was degenerating and we didn't know why. I don’t know if we were ever told the whole truth about it."
The winger managed to get into the All Blacks squad for the Autumn 2002 tour to the UK, but these games were to prove his last in an All Blacks jersey.
He came off at half time in the win over Wales in Cardiff after complaining of double vision and was taken to hospital.
"It was distressing to see this 180kg winger lying on a bed with lots of wires coming out of him," says Mitchell, who now runs a manufacturing business in South Africa.
"If I'm honest, I knew then that this was the end of his All Blacks career."
Mitchell's defining memory of Lomu is of the rampaging, unstoppable teenager he faced in the All Blacks trial in Napier in 1994 though.
The number eight had recently won his first cap, making him the 940th All Black. Lomu was soon to become the 941st, at just 19 years and 45 days of age, making him the youngest All Black in history.
"I remember sitting in a small aeroplane with him going to Napier for that probables v possibles match," Mitchell adds.
"He was a very quiet and unassuming young man, but when he got out of his seat after we landed I thought, 'wow, he's massive'.
"And in the game he was almost unstoppable, he really was. His pace, allied to his size and power, was just unbelievable. He also had soft hands and a lovely balance.
"They named the team after that game and Jonah was in, which was quite something at his age. We all went to the pub afterwards and I can remember going over to him to congratulate him and wish him luck.
"He was very humble and respectful. Who would have known at that stage that he was going to be the star of the World Cup the following year?
"The coach, Laurie Mains, drove him to become even better physically and mentally within the space of just a year. And I don’t think we will see anyone like him again.
"He transcended the sport. He was phenomenal."