Wiremu Lawrence, 15, was killed when the car he was driving hit a tree in Manukau City early on Saturday morning.
Zar Lawrence learned of the news later that morning but, with the blessing of his family, vowed to play on.
The 27-year-old starred with a two-try haul in a 17-5 pool win over Australia last night and scored the only try in their 7-10 quarterfinal loss to Kenya tonight.
Tietjens, who has coached veteran sevens exponent Lawrence for several seasons, had admiration for the player's decision to remain in Hong Kong.
"It certainly has been a tough time for Zar and he gave his very very best. We saw how good a player he is yesterday and then again today," Tietjens told NZPA.
"It was a big decision to stay from both he and his family and we all supported that decision.
"Our chemistry is very close and we did everything we could to win this tournament for Zar and his brother.
"It wasn't to be and we have to keep our heads up."
Manager Ross Everiss was trying to organise a flight home for Lawrence tonight.
Wiremu's body was to be returned to Northland, where a tangi would be held at Whatuwhiwhi, near Doubtless Bay.
Everiss said the tragedy in Auckland had affected all the team while also providing motivation.
"It has had some toll on him, as it would with anybody," Everiss said.
"We were very conscious and aware of the situation and as a team we're very very close.
"Certainly that was part of our motivation to play."
Tietjens was disappointed the team couldn't advance further, their Hong Kong title defence ending after failing to defend an early 7-0 lead against Kenya.
"We're very disappointed. We started well but we didn't really fire a shot after that," Tietjens said.
"I thought we had a team here to win Hong Kong. We showed enough against Australia but we let Kenya back in the game today.
"Kenya are certainly a formidable side now and they played very well."
