The former Tottenham forward scored twice in seven first-half minutes, the first a one-on-one opportunity after being set up by Jonathan Osorio and the second coming following a Seattle error.
It was a perfect start to the new MLS season for player and club and Defoe was delighted to have hit the ground running.
"To score two goals in your debut, it's a dream," he said.
"To come here and to win was massive for us. Everyone's delighted - it was an important three points.
"I said to Jonathan, 'when I make the runs, just look for me,' and he said, 'yeah, I'll look for you straight away.'
"It was an unbelievable pass. I've always worked on those situations, one-on-one with the goalkeeper. You have to be clinical."
Toronto coach and Defoe's former Tottenham team-mate Ryan Nelsen was pleased that the 31-year-old had shown everyone what he can do.
"That was Jermain Defoe," he said. "Let's just say I'm not surprised.
"When the ball falls in those situations, he puts them away. That's why we brought him in.
"I was hoping he'd get in those scenarios and he got in them."
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