Novak Djokovic is out of the world’s top 10 for the first time in a decade, while Andy Murray has slipped to his lowest ranking since 2008.
Serb Djokovic, who has spent 223 weeks as world number one during a career which has brought him 12 Grand Slam titles, first moved into the top 10 on March 19 2007.
Since then he had spent an unbroken spell of more than 10 years inside that elite band but on Monday the 30-year-old dropped out after an injury-hit season.
Djokovic, now 12th, had long since ended his campaign due to an elbow problem, one which forced him to quit his Wimbledon quarter-final against Tomas Berdych back in July.
Both Djokovic and Murray have endured painful seasons and having ended 2016 as the world's top two, the pair now find themselves outside the top 10.
With 2,500 points - earned by winning last season’s Paris Masters and ATP Finals - coming off his record on Monday, the Scot has dropped from third to 16th in the ranking list.
Murray has also been absent from the ATP World Tour since Wimbledon when a hip injury contributed to his quarter-final loss to Sam Querrey.
The good news for Murray and his fans is that he will return to the court this week when he faces Roger Federer in an exhibition match in Glasgow on Tuesday. He is due to be back in competitive action in Brisbane in early January.
In the meantime, 20-year-old Alex Zverev replaces Murray as world number three - a career-high position for the German.
Murray’s slide means that for the first time in 24 years, a British woman has finished a season with a higher ranking than the leading British man. Johanna Konta ends the WTA year ranked ninth in the world.
The previous British woman to do that was Clare Wood, who finished 1993 in 87th place. The top-ranked British male that year was Jeremy Bates (98th).
Meanwhile, Paris Masters winner Jack Sock cracks the top 10 for the first time in his career.
The American, who booked his place in the eight-man ATP Finals field as a result of his victory, is up to ninth. He qualifies for the London event as seventh-ranked Stan Wawrinka is out due to injury.
Filip Krajinovic, the Serbian qualifier who went all the way to the final in Paris, is up 44 places for the week to 33rd.