The Spaniard bore little resemblance to the player who once terrorised his opponents as he slumped to a 6-1, 7-6 defeat by Russia's Nikolay Davydenko.
French Open champion Stan Wawrinka has become the fourth player to qualify for the season-ending ATP World Tour Finals in London.
Factbox on Carlos Alcaraz, who beat Alexander Zverev
Sumit Nagal staged a grand recovery to get the better of Jason Jung of Chinese Taipei 3-6, 6-2, 6-0 and book his place in the quarter-finals of the Chennai Open ATP Challenger in Chennai on Thursday.
Roger Federer's decision to withdraw means Switzerland can no longer take part in the nation-based event on January 3-12
While several top seeds will have their say, a look at some emerging players who could be serious contenders.
Photos from the ATP World Tour Finals matches played in London on Monday
Home favourite Kei Nishikori defeated Frenchman Richard Gasquet 7-6(2), 6-1 in the semi-finals of the Japan Open on Saturday, setting up a final against Russian qualifier Daniil Medvedev.
American Jack Sock clinched the last spot in the ATP Tour finals when he beat Serbian qualifier 5-7, 6-4, 6-1 to win the Paris Masters title on Sunday.
Novak Djokovic has reportedly proposed to move the ATP World Tours Finals from London after 2015 by citing the need to expose the tournament to more cities around the world.
Former world number one Novak Djokovic, the last surviving member of tennis' "Big Four", said he does not plan on stopping any time soon but admitted that the retirement of rivals Roger Federer, Andy Murray and Rafa Nadal has been overwhelming.
World number three Stan Wawrinka beat Roberto Bautista Agut 7-6(8) 6-2 on Saturday and will play Alexander Zverev in the St. Petersburg Open final. The Swiss top seed, playing his first tournament since beating Novak Djokovic to win the U.S. Open title, wore down the Spanish fourth seed Bautista Agut after a tight first set.
World number one Novak Djokovic saw off Canadian Denis Shapovalov 6-3, 6-4 to win his fifth Paris Masters title on Sunday in a warning to his rivals ahead of the ATP Finals, while Ashleigh Barty finished the season in style by beating defending champion Elina Svitolina 6-4, 6-3 to add the WTA Finals title to her end-of-year world number one rank.ing
A season that produced the biggest shake-up in men's tennis for more than a decade draws to a close next week with three ATP World Tour Finals debutants striving to sign off breakthrough years with a large exclamation mark.
Canada's Milos Raonic has withdrawn from the ATP Tour Finals in London due to injury and been replaced by Spain's David Ferrer.
Bob and Mike Bryan thrashed French duo Julien Benneteau and Edouard Roger-Vasselin 6-0, 6-3 to reach the final of the ATP World Tour Finals on Saturday.
The sight of immaculately-dressed line judges standing or crouching at the side and back of the grass courts has been a feature at the Grand Slam for 147 years.
Italy's Sinner and Spain's Alcaraz have won two Grand Slams each this year, with Alcaraz beating Sinner in closely fought clashes at the French Open semi-finals and the China Open final.
Alcaraz returns to action at this week's Cincinnati Open, where he can gain ground on the Serb and Italian Jannik Sinner.
Carlos Alcaraz won two matches to lift Team Europe to a 13-11 victory over Team World for the Laver Cup title in Berlin.
A final decision is expected by March based on the hosting and COVID-19 contingency proposals received from bidders.
Third seed Alexander Zverev produced a near-flawless display to outclass former champion Holger Rune 6-3 7-6(4) on Saturday and return to the Paris Masters final after a gap of four years.
Former champion Naomi Osaka was sent packing from Indian Wells after losing in straight sets to Colombia's Camila Osorio.
Russia's Andrey Rublev overcame Grigor Dimitrov 7-6(7), 6-3 in their semi-final clash at the Shanghai Masters on Saturday, and will now face Hubert Hurkacz, who beat Sebastian Korda.
Eqbal and Faisal's recent success saw him conquer Fardeen Mohammed and Abhinansu Borthakur 6-0, 6-2 in the men's doubles final to win the title.
Defending champion Jannik Sinner dismissed eighth seed Alex de Minaur 6-3, 6-2, 6-1 to reach the Australian Open semi-finals and extend the country's decades-long wait for another homegrown singles winner at the Grand Slam on Wednesday.
Jannik Sinner retained his Australian Open title with an emphatic 6-3, 7-6(4), 6-3 win over Alexander Zverev on Sunday
Rafael Nadal produced one of his best performances of the year to beat Andy Murray 6-4, 6-1 at the ATP World Tour Finals and move within sight of the semi-finals on Wednesday.
Dominic Thiem stayed very much in the mix at the ATP World Tour Finals with a 6-3, 1-6, 6-4 victory over mercurial Frenchman Gael Monfils at the O2 Arena on Tuesday.
The Indian has won five ATP Masters 1000 titles with five different partners, although he has never won a major championship in men's doubles. Not bad for someone whose knees lack cartilage.
Novak Djokovic's bid for a 100th ATP Tour title gained momentum on Thursday
After registering a runner-up finish in the Qatar Open, Andy Murray set himself a target of registering 800 career wins.
Rafael Nadal won two Grand Slams this year -- the French Open and the US Open -- to move within one of Roger Federer's record of 20 titles.
World number one Nadal will meet Greek teenager Stefanos Tsitsipas in Sunday's showpiece when he will target a record-extending 11th title in Barcelona a week after claiming the Monte Carlo Masters for the 11th time.
Defending champion Dmitry Tursunov fought back from a set down to upset top seed James Blake 4-6, 6-3, 6-4 and reach the final of the Indianapolis Championships on Saturday. The Russian will now face Gilles Simon after the Frenchman reached his first career ATP final in the United States with an exciting 6-3, 4-6, 6-4 win over local favourite Sam Querrey.
Medvedev will be glad to play the role of dream wrecker once again.
Nikolay Davydenko beat weary Argentine Juan Martin del Potro 6-3, 6-4 to claim the ATP World Tour Finals title at the O2 Arena on Sunday. The wiry Russian, who has climbed to sixth in the world this week, produced a faultless display to claim the biggest title of his career and a $1.5 million cheque.
-French flair topped American firepower as Gael Monfils turned back the clock to dump fourth seed Taylor Fritz out of the Australian Open on Saturday and celebrate his place in the last 16 with a dance on court.
Djokovic helped Serbia to a 3-0 victory over Japan in their Group A opener on Wednesday at La Caja Magica where a revamped Davis Cup climax is being contested by 18 nations over seven days.
