The reigning 800m national champion was a surprise winner on the opening night of competition at Sydney Olympic Park, slashing more than a second off her previous PB in the event.
The 18-year-old clocked 1 minute 57.38 seconds, to hold off Bronte Barratt (1:57.46), Kylie Palmer (1:57.69) and Stephanie Rice (1:58.13), who teamed up to claim gold in the 4x200m freestyle relay in Beijing.
"That's a massive shock to me," Evans said.
"The 200 was always going be one of the pre-trial events for the 400 and 800 but to be able to come out on top in the 200 over some of the best girls in Australia is an amazing feeling for me."
Evans put her improvement down to a new and improved attitude and said her shock win bode well for her pet events.
"After this, I think I'm in for a big competition over all the events, which is really exciting," said Evans, who will contest the 800m heats on Thursday.
Rice (2:10.07) earlier showed young challenger Emily Seebohm (2:10.75) she was still the medley queen by mowing down the teenager in the final lap.
But Rice admitted to her concerns about the threat from Seebohm.
"0.7 is not a big difference and for someone so young who is always improving she has been on my radar for the last two or three years, she has really come through," Rice said.
As expected, the times were a bit off the mark from the past few years where supersuits have savaged the world record books.
Nick D'Arcy, meanwhile, has always found a reason to keep on swimming, no matter the setback.
So with the words of his late grandmother urging him on at the Commonwealth Games trials in Sydney, he was never going to be headed in the 200m butterfly.
Doreen D'Arcy died last week and her grandson proudly dedicated his third straight national title in the event to her memory.
This time there is a difference, a major international meet with the national team beckons.
Sure, he still must convince US consular officials next week to let him compete at the Pan Pacs in California because of his criminal conviction.
But national head coach Leigh Nugent hinted on Tuesday that Swimming Australia could use their discretion to select him for the Delhi Games even if he is barred from the US.
"If we got to that point, that might be the case," Nugent said.
D'Arcy (1minute 54.61 seconds) said his grandmother had spurred him on to keep swimming despite his disastrous past two years in which he was booted off the 2008 Olympic and 2009 world championships team for assaulting former swimmer Simon Cowley.
"That was a little bit tough, she got a little bit sick and we knew it was coming and I thought she would be around just for this," he said.
"It has been a big stretch and she always calls me up when I do well.
"She was always telling me to keep going and she has been a huge support.Felicity Galvez (1:58.23) and Meagen Nay (1:58.62) also look to have booked their spots on the team for October's Games and the Pan Pacific Championships in the US in August, with the top six likely going through.