Like the best recipes, sometimes the missing ingredient is not apparent until it is added - and de Bruin has brought a lot to the table.
"She is so committed to being better," coach Noeline Taurua told the Herald on Sunday, "and it permeates through the team. Her work and training ethic is probably second only to Laura [Langman].
"She has brought mongrel, hardness and a new level of communication. It is a point of difference and closes a gap that I had identified."
Among defenders, only Laura Geitz has grabbed more defensive rebounds, while de Bruin is second in the league for deflections and seventh for intercepts.
Things are running smoothly now but for a while, de Bruin struggled, both with her role and the partnership with Williams. Despite her experience - de Bruin has been a Silver Fern for a decade - it wasn't easy joining a team with such established stars.
"I was a bit nervous," remembers de Bruin. "At the Steel, I was the big cheese but this team already had the three top dogs. It is quite a hard environment to come into."
Like the rest of her team, de Bruin struggled to find her groove at the start of the year. She was trying too hard and couldn't gel with Williams, frustrating for both.
"Both of them were No 1 players," says Taurua, "and we needed to find the link that would highlight their individual skills but also complement each other."
It is not a problem unique to netball. Bringing stars together can have less than dazzling results. Like the 1999 All Blacks, where John Hart tried to shoehorn Christian Cullen, Jeff
Wilson, Tana Umaga and Jonah Lomu into one backline. Gary Freeman and Clayton Friend never combined well for the Kiwis while, despite their unquestioned talent, footballers Steven Gerrard and Frank Lampard have rarely shone in tandem for England.
"[Casey] always told others where to go," says de Bruin, "and suddenly she had a bossy one at the back. I told her she had to trust me and listen to what I say - most of the time, it will be right."
"Leana is probably the only one in the team who can give Casey a bit of 'what for' if something is wrong in the circle," says Taurua. "They are both straight talkers."
De Bruin admits they are quite hard on each other and there are some "testy moments" but everything is left on the court.
"Sometimes I look back at Casey and see the 'angry bird face'," says de Bruin. "That's when I know that we are about to go to another level."
It helps that the two have a unique relationship that stretches back to when Williams was an unknown teenager. When de Bruin first arrived at the Magic almost 10 years ago, she would pick up Williams from school and they made their way together to Magic training. From a country background in South Africa, she also relished the chance to spend time on the Williams family farm.
"We would hang out there and milk the cows," remembers de Bruin. "It was great to get some farm dirt on my hands."
The strength of the partnership came to the fore in the final minutes of last Monday's preliminary final. Earlier in the fourth quarter, their attack was floundering amid incredible pressure from the Mystics defence - but Williams and de Bruin, together with Langman and wing defence Elias Shadrock, kept their team in the hunt, then dragged them back into the match with crucial plays.
"I had to watch the game again last week," admitted de Bruin, "because I didn't know how it happened. Our intensity lifted a little in those final moments.
"I remember looking in Casey's eyes and she had flicked a switch. We tried to really confuse the shooters and get in their heads. [At the end] all I was thinking was, 'I gotta get my hands on that ball'."
"Her impact on that match was incredible," says Vixens defender Julie Corletto. "She helped to turn the end of the game."
Both are looking forward to the grand final, when the Magic hope it will be third time lucky in an ANZ Championship decider.
There are crunch battles across the court but surely the New Zealand side will target the Vixens attacking end, which is relatively inexperienced and the obvious Achilles heel.
"They have been a bit lucky to win sometimes this year," says de Bruin of the Vixens, "but they have been a little like us. They keep finding a way to win. Their shooting circle is inexperienced but they have grown in confidence. They can be frustrating to play against. They are safe with the ball and we don't know a lot about them. But we'll find a way to get into their heads."
