Although Sail downplayed the ailment – "just a heavy cough" – he was far from 100 per cent.
"I decided not to train [on Wednesday], because that was probably when I was feeling worst. So I let it settle down for the day and just spent all of [Thursday] in bed and got up to eat mid-afternoon and prepare for the game."
He never considered not taking his place between the posts.
"There was a lot on the line," said Sail. "And from a leadership point of view as well I felt like I had to be there. There was no doubt in me playing."
Sail's effort epitomised the spirit in this Phoenix team, who have overcome an extraordinary number of obstacles.
They were written off by most pundits before a ball was kicked, with a green-looking squad following the loss of several influential players.
That sense of doom had heightened by round 10, when they were bottom of the table, but they have rebounded to reach the top six ahead of clubs with much greater resources.
And they've done it despite all kinds of dramas, with Covid outbreaks, untimely injuries and an unprecedented match schedule.
That took its toll with some heavy losses - the Phoenix have conceded a staggering 36 goals across their 10 defeats – but they have always found a way back.
Sail admitted it had been a "psychological and emotional rollercoaster" at times, but the inexperience within the group had provided a silver lining.
"The beauty of having such a young squad is that they're blissfully unaware about the situation around them," said Sail. "They don't comprehend a lot of the pressures, the external pressures, which is brilliant."
Oli Sail overcame illness to help the Phoenix book their place in the playoffs. Photo / photosport.nz
Sail also paid tribute to coach Ufuk Talay, who juggled his resources superbly, got his tactics spot on when it mattered and infused belief in his players, even when all seemed lost.
Sail couldn't hide his enthusiasm as he contemplated finals football next weekend.
"As we have shown this year, there's no one we can't beat on our day so going into playoff football with [this] squad is pretty exciting," said Sail.
The Phoenix could finish as high as fourth but would need to beat Melbourne City on Monday and hope both Adelaide and Central Coast drop points this weekend.
But the most important part of the job is done. Talay told his players to "write their own destiny" before the Wanderers match, rather than relying on other results to ensure post-season football.
They achieved it in a wildly entertaining game, with the Wanderers determined to atone for their recent Eden Park defeat.
A sumptuous 65th-minute strike from Reno Piscopo proved the difference, after Sam Sutton put Wellington ahead with a fine volley before Tomer Hemed equalised against his old side.
The Phoenix hit the crossbar twice before halftime, while a second-half Ben Old effort was ruled out by a fractional VAR offside call.
Sail came to the fore in a gripping finale, pushing two goal-bound shots onto the woodwork as Wellington hung on.
"I was pleased with the boys' discipline, in grinding it out at the back end of the game," said Talay. "And sometimes we need that rub of the green as well. We got it but it was a good performance."
