Novak Djokovic faces Dominic Thiem at The O2 on Sunday as he begins the defence of his World Tour Finals title and his pursuit to reclaim the world No 1 ranking. Djokovic saw his 122-week hold on top spot ended last weekend when he was usurped by Andy Murray as the worlds top ranked player. World No 1 permutations How the No 1 ranking can change hands...again Having previously admitted that his desire and love for the game had waned, it may be that this latest development adds fuel to the Djokovic fire as he looks to win a sixth World Tour Finals and end the season on top of the standings once again. The 29-year-old has won the season-ending event the last four years and is a two-time Grand Slam champion this year, winning the Australian and French Opens to take his career tally to 14 major titles. Djokovic has endured a frustrating second half of the season and has lost his world No 1 ranking to Andy Murray He also owns a dominant 23-0 record against his three rivals in the Lendl group and first to challenge that will be the youngest man at this weeks finals - Thiem. Ivan Lendl Group Novak Djokovic (Serbia) Milos Raonic (Canada) Gael Monfils (France) Dominic Thiem (Austria) World Tour Finals: Profiles We look back on the year so far for the eight contenders Thiem too has had his struggles over the second half of the year but claimed four titles over the course of the regular season The Austrian is making his debut at the event and after a sensational start to 2016, tailed off over the second half of the year.He has never won a set against Djokovic, losing all three meetings including their most high-profile encounter at the French Open semi-final earlier this year where Djokovic won 6-2 6-1 6-4.In recent weeks the 23-year-old has suffered surprise defeats to Jack Sock, Viktor Troicki and Alexander Zverev and has not gone beyond a quarter-final since the middle of September. Introducing the underdogs What do we know about debutants Dominic Thiem and Gael Monfils However Thiem is not to be underestimated having claimed four titles this year, only Murray (eight) and Djokovic (seven) have won more although the last of those came back in June.Djokovic too has wobbled since his dominant first half of the year - he has been beaten by Marin Cilic and Roberto Bautista Agut since using the US Open final to Stan Wawrinka and he has won just one title since completing his career Grand Sam at Roland Garros and that came with victory at the Rogers Cup in Toronto in July.Whether Thiem can capitalise remains to be seen but the opening singles match of the tournament promises to be an intriguing one. World Tour Finals: The Groups We run through the contenders and their groups at The O2 As is the case for every session the doubles will kick off the action from 12pm on Sky Sports and the first match of the week will see Mike and Bob Bryan taking on Ivan Dodig and Marcelo Melo. Edberg/Jarryd Group Bob Bryan & Mike Bryan Ivan Dodig & Marcelo Melo Jamie Murray & Bruno Soares Treat Huey & Max Mirnyi Bob and Mike Bryan are five-time winners of the season-end doubles event The American brothers are seeded third this year and are four-time champions of the event but come into the tournament on the back of two years without a major title.They face sixth-seeded pair Dodig and Melo who have won the last two Masters events they have entered in Cincinnati and Canada.All the action from the O2 between November 13-20 will be live on Sky Sports across the week and if you are out and about you can follow on our Sky Sports apps and the website via our live blogs. Full schedule here. Live Tennis: ATP World Tour Finals November 13, 2016, 12:00pm Live on Get Sky Sports Get a Sky Sports pass Also See: The Groups Shots to watch Tour Finals at The O2 Panel Predictions Hydro Flask Sale .com) - Even-money favorite Liams Map proved a little too tough down the stretch and won Saturdays $100,000 Harlans Holiday Stakes at Gulfstream Park. Hydro Flask 24 Oz Sale . While he was away, it was the division-rival Baltimore Orioles conducting a little business of their own, scooping up Ubaldo Jimenez on Monday evening to a reported four-year, $50-million contract. http://www.hydroflaskombrecanada.com/hyd...wide-mouth.html. Both the top-seeded Djokovic and sixth-seeded Fish took relatively easy paths, with the Serb winning when opponent Jo-Wilfried Tsonga retired in the second set with a sore arm and Fish dominating Janko Tipsarevic in two quick sets. Hydro Flask Canada . That still leaves a big hole.You dont replace the leadership, defensive co-ordinator Billy Davis said. You just dont. Leadership is something that is earned over time. Hydro Flask 21 Oz Canada . His absence against the Celtics comes a day after he scored 43 points in the Heats 100-96 win at Cleveland.Romain Grosjean has been given a new chassis for the Monaco GP by his Haas team. After scoring points in the first two races of the season, the team have struggled over the last month, culminating in an irate Grosjean describing his car as undriveable during the Chinese GP when he finished just 19th.The team have now heeded Grosjeans complaints - with the Frenchman still unhappy with how the front end of his car behaved in Barcelona two weeks ago - by providing him with a new chassis for this weeks Monaco GP. Everyone is trying to get the chassis to what it was, Grosjean told Sky Sports News HQ.We changed the chassis to come here to make sure there is no doubt about it, and we did some good testing in Barcelona after the race, so Im hopeful I can jump in the car, get some good sensations, and come back for a good grand prix. Team-mate Esteban Gutierrez, who has yet to score a point since returning to F1 with the Haas outfit, will continue with his previous hub.Grosjean, meanwhile, will wear a helmet dedicated to the memory of Jules Bianchi, the former Marussia driver who died last July from injuries sustained at the 2014 Japanese GP, this weekend. Five monthss before his crash at Suzuka, Bianchi had scored Manors first points in F1 at the 2014 Monaco GP.dddddddddddd.Jules is still one of us, said Grosjean. He was a good friend. He did an amazing race here back in 2014, he scored the only two points for Marussia. I wish I could have gone for the full [helmet] design, but the rules changed a little bit.Hes always with me on the helmet and I want to keep it [that way] until the end of m