Patrick Mouratoglou has made very few mistakes since taking over as the coach of Serena Williams in June 2012, since when the American has won nine of her 23 Grand Slam titles.

The Frenchman is known for his attention to detail ... from studying video to planning strategy. But, as Williams prepares to face her sister Venus in the final of the Australian Open, he will be making sure of one thing, in particular.

“To tell you the truth the first time they played each other, when I was coaching her, I didn’t really know what to do and so I was very light in my words before the match and Serena lost,” Mouratoglou said.

It was in Montreal in 2014 that Venus beat Serena in three sets, a result that annoyed Mouratoglou intensely, something he remembers well.

“I said to myself it’s my fault, I should have treated Venus like any other player,” he said. “They’re on a tennis court, they’re competing, they’re sisters, OK, but someone has to win and if someone has to win it has to be Serena.

“It was a good lesson for me and, since that day, I’m doing the pre-match talk exactly as if I didn’t know Venus and Serena didn’t know Venus.”

This will be the 28th meeting between the two sisters, with 36-year-old Venus into the final of a Grand Slam for the first time since 2009 and trying to become the oldest woman to win a Grand Slam title in the Open era.

Serena leads their head-to-head record 16-11, and 6-2 in their eight grand slam finals and victory will give her an Open era record 23rd grand slam title.

At 35, world No.2 Serena is a year younger than Venus, who has had a new lease of life in the past 18 months and fully deserves her place in the final.

Some of the finals between the two have been flat, others have been intense, and the two sisters will share a hug at the end, no matter what.

Mouratoglou, though, is focused on preparing the six-times Australian Open champion as well as possible to be ready for a unique, if familiar challenge.

“Even though Serena knows Venus very well, she likes me to scout and give her my feelings,” he said.

“Even though you know a player well – the technique doesn’t move so much – but, from one tournament to another, sometimes there is a pattern of play that works well in a tournament and subconsciously a player will do it much more than normal.

“So those things you have to find out, so those things you have to scout. You should always scout before a match.”

Former world No.1 Jim Courier said yesterday he felt Serena had the edge but that it will come down to who can shut out the opponent the best.

“The most they can stay in the silo the better,” the American said. “I imagine it’s crazy challenging to do, but if they can play the balls then it becomes a more compelling match than if it’s ‘that’s my sister over there’, which we’ve seen, a lot.

“They’ve had flat matches before that have been drama-free and tension-free. But history is on the line for both. For Venus too. She’d be the oldest woman to win a major if she wins. Serena is the current holder so, either way, that record gets extended in the one family, which is just jaw-dropping to think about.”