Andy Murray will aim to make it three wins out of three for British players when he meets Novak Djokovic in the standout match of the group stages at the Barclays ATP World Tour Finals in London on Wednesday.
The world number three began his campaign on Monday with a three-set victory over Tomas Berdych, and a repeat against Djokovic could book his place in the semi-finals.
Murray and Djokovic have met six times already this year, winning three each, and the key feature of the battles between the two is that they have been just that: brutal battles to the point of exhaustion.
"For me there's an understanding of how much you have to put into the match to win it. I think that's just the nature of these matches," Murray said.
"Both of us are very good retrievers, so often the points will go on a lot. Sometimes you feel like you need to win the point two or three times, which is tough and can be a little bit tiring.
"But we've played each other enough to know what to expect."
Both their grand slam meetings have lasted almost five hours, with Djokovic coming out on top in the Australian Open semi-finals before Murray turned the tables to win his first grand slam title at the US Open.