The three-time NBL champion recovered from illness to help the defending champions take the honours in Tuesday's grand-final rematch at John Cain Arena.

Cotton steered Perth home in the second half with a series of key baskets to finish with 30 points and nine assists as Perth became the first team to win their opening two NBL Cup games.

"We didn't even know he was going to play until an hour and a half before the game started," coach Trevor Gleeson said after Cotton's match-winning effort.

"He wanted to play, he didn't want to let his teammates down ... it's just a testament to what kind of person he is, a selfless person that will get out there and play.

"To put in a performance like that when you're not 100 per cent, you tip your hat to him."

Centre John Mooney took full advantage of Sydney's limited frontcourt stocks to match Cotton with a career-best 30-point haul to go with 16 rebounds.

Sydney set the pace in a high-scoring opening half before the Wildcats pounced in the third quarter with a 32-17 run to seemingly take control of the contest.

But the Kings refused to concede as they fought back to trail by three points in the final minute, Casper Ware leading the charge with a game-high 34-point effort.

With the result on the line, Cotton and Mooney each sank two free throws to end Sydney's comeback.

The Kings jumped out to a 30-24 lead thanks to 11 first-quarter points from Ware before Didi Louzada caught fire in the second term, the Brazillian NBL Next Star making 6-of-8 shots, including four three-pointers, in his 16-point first-half haul.

A late flurry from the Wildcats reduced Sydney's advantage to 56-54 by halftime and Mooney kick-started Perth's third-quarter blitz with five quick points before Cotton nailed his first triple of the night to extend the lead to 79-66.

Kings coach Adam Forde lamented his side's tentative play following some early foul trouble but expects they will become more composed under pressure as the season rolls on.

"It's definitely a learning point for us because we are relatively new coming together and finding out what our strengths and weaknesses are," Forde said.

"That third quarter, we are definitely going to take some teaching points from it."

Australian Associated Press