It felt as though Sun was chasing the match from the start – with an early first-set break – though she had momentum after squaring the match, following a rain delay of almost 90 minutes.
But she fell into another hole in the third set, giving up consecutive breaks to trail 5-1.
The world No 40 never stopped fighting – with the crowd willing an improbable comeback – and saved two match points, before No 102 Marino converted her third.
It’s a setback for Sun, who wanted to make an impression here, and her disappointment was obvious as she left the court, head bowed.
After her amazing 2024 season, where she climbed from outside the top 200 to No 40, there was plenty of expectation on the 23-year-old.
New Zealand tennis fans had been waiting for a local hero and wanted Sun to fit that bill.
The Te Anau-born player was aware of that billing, coming onto court in a new all black outfit and getting a good reception.
But she made a nervy start, especially on the backhand. Marino was unleashing service bombs and backing those up with powerful forehand drives.
The swirling wind didn’t help matters, seeming to affect Sun more. She gave up a break in the fourth game of the opening set – with a couple of unforced errors – and Marino was never headed from there. Sun couldn’t settle, not helped by the number of short rallies.
She looked frustrated and after she sent a forehand miles long at the start of the sixth game she leaned back on her hips in exasperation, as if to say, ‘what is happening here?’
There were positive signs – with a couple of strong holds – including a sizzling backhand winner, which got her going.
But Marino kept serving her way out of trouble. Sun was persistent, coming back from 0-30 to 30-30 at 5-3 to pressure the Canadian. But Marino got to set point – aided by a timely net cord – sealing the bracket with a deep ace.
Sun had to respond and began to make inroads on the Marino serve. The Canadian saved two break points in the second game but momentum was building, and it was no surprise when Sun broke for a 3-1 lead, then held after one of her best points of the afternoon.
The rain delay felt unfortunate, but Sun was quick to restart and evened up the match from her second set point.
But the sweet and sour continued. Sun was broken early – not helped by two double faults – though broke back immediately, prompting one of the biggest cheers of the afternoon.
But she immediately fell into another hole – with more problems on serve and was broken in consecutive games to trail 5-1. Just when it looked completely forlorn, Sun found some form, starting to dominate points and hit the lines.
With a break and tough hold, she climbed back to 5-3, with Marino under some pressure. That intensified as the Canadian was down 15-40, after a well-placed winner.
Marino scraped back to deuce, then had match point.
A strong return saved one, an audacious drop shot another, but there was no miracle on the third.
Michael Burgess has been a sports journalist since 2005, winning several national awards and covering Olympics, Fifa World Cups and America’s Cup campaigns.