It was the second match it four days for the Sky Blues and by the end of their 2-1 victory at Allianz Stadium on Tuesday night both sides were out on their feet.
But Arnold was determined that Adelaide United would be the last to know if his men were struggling.
At the end of regulation time, and with the scores deadlocked at one apiece, he urged his players to keep it together.
"One of the things I said - don't show them you're tired even if you are," Arnold told Fox Sports.
"It's about showing them we're strong. We looked at them, they were on the ground, it gave us a bit of energy."
Milos Ninkovic (19') opened the scoring for Sydney and Bobo (111') sealed the win in extra time after Nikola Mileusnic (67') levelled the scores.
The win goes some way to erasing the pain of losing the decider to Melbourne City last year.
Reigning Premiers and Champions, Sydney now have the complete set of trophies for 2017 and multi-title winner Arnold has finally clinched the one missing from his CV.
"It was an outstanding effort with only a three day turnaround from the last game and 120 minutes," Arnold said.
"It just shows you the mateship and camaraderie in this group that they fight for each other and they believe in everything we do.
"For me that's the first of three trophies. It's the third in the calendar year, and it's a great achievement, but our motivation, our drive is the second one and that's the (2017-18) Premiership."
The Sky Blues will head into their home game against Brisbane Roar on Saturday with some injury concerns.
Ninkovic was subbed just after the hour with a calf strain, while winner of the Mark Viduka Medal Adrian Mierzejewski and Luke Wilkshire both struggled late on. Defender Michael Zullo admitted it was tough going.
"I've definitely finished games feeling better but it's all going to go away I think when we get back in the change room and look down at the medal," he said.
"It's massive for me personally and massive for our whole team. It's a trophy the club hasn't won (before). It's a big part of the team to make history, that's what all players want to do and like I said I'm so proud to be part of it."
Zullo said Arnold's extra time talk spurred them on: "The message pretty much from him was 'just look at them'. They were all the floor getting treated and we were all standing up feeling strong.
"We played a game (three) days ago and we still managed to go the 120 minutes. It was pretty much just go out there and win it - we're winners, prove it. And I'm so happy."
But there will be no time to celebrate just yet with the A-League table toppers keen to maintain their league run.
Arnold said: "We'll find a date that we can celebrate but for now it's about being professional and putting in a great performance against Brisbane, which we will."