The 32-year-old world No1 lost her serve twice in the second set but broke back three times to emerge victorious in 98 minutes.
I’m really, really happy with the way I played and the intensity level
Williams has now won 22 consecutive matches since losing to Azarenka in the Cincinnati final.
She has also won 34 of her last 36 matches against top-five players, with her only defeats in that period, which dates back to Wimbledon 2011, coming against Azarenka.
“I’m really happy here and I love coming here to Brisbane,” said Williams. “I’m definitely excited to have won and I’m really, really happy with the way I played and the intensity level.
“It’s definitely always interesting to play someone like Victoria – I know her game, I know what she does – but she goes out and improves, so every time I go out there and play her, things I thought were her weaknesses are now her strengths.”
Azarenka, whose record in WTA finals falls to 17-15, said: “I want to congratulate Serena on a great week and a great match today.
“I always enjoy playing you and I hope to meet you again in Melbourne. Since my first year here I’ve had such good memories and I’ll take some from this year too.”
Williams’ win marks the 58th title of her career, 14 more than any other active player and the seventh-most in history.
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