Blues coach Lam said he was determined to give Anscombe that job only when halfback Weepu and second-five Nonu, who was making his Blues debut after a delayed start to the season, were alongside him.
"It was an outstanding effort. We've known he has a lot of talent but we wanted to nurture that and play him when the time was right," Lam said.
"For [assistant coach] Bryce Woodward and myself we purposely waited for Ma'a to get here and Piri to start so to play in between those two was a big help for him."
Anscombe agreed. "They both have a lot of knowledge of the game.
"When we came together and talked it made my job a lot easier.
"I would put it right up there," he said of his experience. "It's a daunting place to play up here but I tried not to think about it too much."
Anscombe didn't have to wait long to be involved.
After only two minutes he was the beneficiary when the Bulls' inside backs made a mess of a simple move and he ran in from 50 metres.
He struck again two minutes from the end of the first half when running on to an excellent pass from prop Pauliasi Manu to score another seven pointer.
Blues 29 (Gareth Anscombe 2 tries; Anscombe 2 cons, 5 pens) Bulls 23 (Bjorn Basson 2, Pierre Spies tries; Morne Steyn con, 2 pens). HT: 20-8.