Novak Djokovic crushed Tomas Berdych 6-2 6-2 to reach the last four of the World Tour Finals and clinch the year-end No.1 ranking.
Djokovic secured an immediate double break and wrapped up the first set in just 31 minutes, securing his place in the semi-finals at the O2 Arena.
The second set began the same way as Djokovic raced into a 4-0 lead before completing the rout in one hour and nine minutes, racking up his 30th straight win indoors, a streak which extends across three seasons.
“It’s a great deal of happiness knowing that what I’ve been through the entire season in order to get to where I am and finish the year as No.1,” said Djokovic. “I owe gratitude to my team, to all the people who were next to me.
“It’s one of the ultimate challenges. Being No.1 of the world is the pinnacle of the sport.”
It is the third time in four years that Djokovic has finished the year at No.1, as he chases a third consecutive World Tour Finals title.
In 2014, he claimed his seventh grand slam at Wimbledon, and has won other six titles, including four Masters crowns in Indian Wells, Miami, Rome and Paris.
“One of the highest and most difficult challenges is to be No.1 nowadays, especially because the tennis has become very competitive in the last five, 10 years, very physical,” added Djokovic. “To have a shot at No. 1 of the world, you need to be consistently healthy and successful throughout the year.
“Because [Rafael] Nadal and [Roger] Federer are so good for so many years, they always make you win at least one or two grand slams if you eventually want to be No.1, and of course with consistency, because they’ve been so consistent with their results. I know how difficult it is. It’s why I’m proud of this achievement.”
Djokovic now faces Kei Nishikori in the semi-finals on Saturday and is anticipating a battle.