It was the third year on end that Williams, 23, has taken out the 100m-200m-400m combination and she was in commanding form today, clocking 23.15 seconds to take the title streets ahead of second-placed Anna Smythe (Otago) in 24.01sec.
Williams' time easily broke the New Zealand resident record of 23.26sec she set two weeks ago in Christchurch.
Earlier this season, Williams bagged Kim Robertson's 31-year-old national 200m record when she ran 22.98sec to beat the A standard for the world athletics championships in Berlin later this year.
Williams is also closing in on Robertson's national 400m mark of 51.60sec, with a 52.20sec to her credit at the Melbourne grand prix three weeks ago. Today, however, Williams was just pleased to have kept her focus and picked up her third sprint treble, continuing a recent run of particularly consistent form.
"I'm quite glad to be really consistent and back up all my times," she said afterwards.
"It's more pressure from myself -- I just tell myself I've got to run fast, it's all on me. But I'm pretty good with the pressure."
The wind reading for the race was nicely under the legal two metres per second at 1.8m, but Williams had to work hard into the blustery Wellington northerly battering the curve into the home straight.
"The first 50 metres is a head win, but if you can get the good tail wind down the home straight it really helps." Williams has had a busy few days, winning her least-favoured 100m on Friday with a personal best 11.64sec then taking yesterday's 400m title in 54.08sec.
Helped by both 400m and 200m being run as straight finals, Williams said she still had a little stiffness to work out of her legs going into today's final event.
"I was a little bit sore warming up, but it usually feels like that anyway, so you've just got to push through it."
Although the New Zealand season has now wound up, Williams won't be easing off too much, with the world championships now a top priority.
"I've got a couple of weeks' rest than back into a little bit of base training, but I'll be trying to keep in touch with my speed so I don't lose that."
In the men's 200m today, 100m winner Carl van der Speck was beaten into third by Auckland teammate Jeffrey Thumath, who mowed down the field over the closing stages for a 21.09sec win.
Defending champion James Dolphin took second in 21.18sec.
