The Argentine world number five took just 53 minutes to master the Australian defending champion 6-3, 6-1.
It was del Potro's 18th career title and he became the first Argentine to win in Sydney since David Nalbandian in 2009.
It was the ideal lead in to Monday's Australian Open for del Potro, who plays a qualifier in the first round and is seeded to face world number one Rafael Nadal in the quarter-finals.
"Finals are never easy, but I was surprised at my level of play tonight. I think I played great," del Potro said.
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The big Argentine served eight aces and broke Tomic's serve four times for a comprehensive win.
"To start the year in this way it's very positive looking forward for the rest of the season. I need to keep working in the same conditions and the same way.
"Now it's the hardest tournament for us, and I will see if I can go further than last year (third round) in Melbourne.
"After two or three matches I started to play much better. My movement was faster than in the first rounds here."
"I think Bernard was a little frustrated after seeing me very focused on the match and hitting the ball so well," the Argentine said.
"He is still young, but he has everything to win titles, and he will reach more finals very soon.