City peppered Waitakere with waves of dangerous attacks, but their defence held firm, led by Strasser and Julyan Collett.
"We had most of the possession and created a ton of chances but we just couldn't finish. But fair play to Waitakere they scored their goal early because we hadn't switched on. After that they parked a great bus, to be fair," said Auckland City skipper Darren White.
"I hope this is a wake-up call for us because anyone can beat anyone in this league on the day," said White, perhaps forgetting that Southern United are in the league.
The loss is a rarity for Auckland, who had gone 28 games unbeaten before losing to Team Wellington in last year's final, making it two straight defeats for the usual Premiership frontrunners.
Auckland take on Wellington in a final re-match next week as the first full round of the Premiership gets underway, while Waitakere visit Hawke's Bay. The slate also sees the Wellington Phoenix Reserves host Eastern Suburbs, Canterbury United play Tasman United and Hamilton Wanderers face Southern United.
Waitakere United 1 (Harrison Nash)
Auckland City 0
Halftime: 1-0