Lionel Messi has already confirmed this World Cup will be his last and his final campaign on the biggest stage starts with Argentina on Tuesday.
Messi will lead La Albiceleste against Saudi Arabia at Lusail Iconic Stadium in the first of four matches to be held on day three in Qatar.
Argentina's other Group C opponents, Mexico and Poland, play later in the day.
The first two Group D games see Denmark take on Tunisia and holders France cap off the action against Australia.
Here, with the help of Opta data, Stats Perform makes some key predictions ahead of Tuesday's matches.
All times local.
Argentina v Saudi Arabia – Lusail Iconic Stadium (1300)
Messi will be eager to get his World Cup swansong off to a flying start and Saudi Arabia should present the ideal opponents for Argentina in that regard. They featured in the opening game of the 2018 World Cup and were thrashed 5-0 by hosts Russia. It's not a stretch to think they could be on the receiving end of a similar result against a much stronger side.
Saudi Arabia have won only three of their previous 16 World Cup matches, while they have failed to score in nine of those matches (56 per cent), the highest such ratio of any Asian side to play five or more games in the competition.
Though they come into this tournament as one of the favourites, Argentina have lost three of their last five matches at the World Cup (W1 D1), as many as in their previous 24 combined (W16 D5). They suffered two defeats at the 2018 edition (3-0 v Croatia, 4-3 v France), the first time they had lost multiple games in a single tournament since 1994.
Player prediction – Messi's group-stage love-in to continue: All six of Messi's World Cup goals have been scored in the group stages, with the superstar never finding the net in 756 minutes of play in the knockout phase of the tournament. Given Saudi Arabia are nowhere near Argentina's level, the Paris Saint-Germain forward should be licking his lips.
Best bet – Argentina to score at least three goals: Saudi Arabia are on the joint-longest run without a clean sheet at the World Cup (13 games), conceding 36 goals across those 13 matches (2.8 per game).
Denmark v Tunisia – Education City Stadium (1600)
Euro 2020 semi-finalists Denmark built their qualification campaign on solid foundations, keeping eight clean sheets, more than any other team in European qualifying.
Tunisia cannot be fancied to keep sides out on many occasions, though – they have not had a shutout in 14 of their 15 games at the World Cup, the only exception coming against Germany in 1978 (0-0).
Denmark are unbeaten against African opposition at the World Cup (W2 D2), while Tunisia have never prevailed against European opposition at the tournament (D3 L7).
Player prediction – Wahbi Khazri to shine: If Tunisia are to find a way through Denmark's defence, Wahbi Kazri is likely to be crucial. He has been directly involved in each of Tunisia’s last four goals at the World Cup (two goals, two assists).
Best bet – Denmark to avoid defeat: The Danes are unbeaten against African opposition at the World Cup (W2 D2), while Tunisia have never prevailed against European opposition at the tournament (D3 L7).
Mexico v Poland – Stadium 974 (1900)
Poland have only won one of their eight previous opening matches at the World Cup, way back in 1974. That should be good news for Mexico, who have won five of their last six such games.
Mexico goalkeeper Guillermo Ochoa was the only player to feature in all 14 of their qualifying matches for the 2022 World Cup. He has played each of the nation's eight matches in the finals across the last two editions (2014 and 2018) and could become only the second Mexico goalkeeper to make an appearance in three separate World Cup tournaments, after Antonio Carbajal (five from 1950 to 1966).
Mexico kept more clean sheets during the third round of CONCACAF qualifying for this World Cup than any other nation (eight), with only table toppers Canada (seven) conceding fewer goals at that stage (eight).
Player prediction – Robert Lewandowski to score anytime: Robert Lewandowski had a hand in 13 goals in World Cup 2022 qualification (nine goals, four assists), more than twice as many as any other Poland player.
Best bet – Poland to score from a set-piece: Poland's last five goals at the World Cup have come from set-pieces (three from corners, two from indirect free-kicks). Their last goal from open play at the tournament was 20 years ago, by Pawel Kryszalowicz against the United States.
France v Australia – Al Janoub Stadium (2200)
Les Bleus beat Australia 2-1 in their opening game in 2018 and the reigning champions are big favourites for this one, though the Socceroos have some hope, given the holders have won their opening match in just three of the last 12 editions of the World Cup.
Each of Australia's last three World Cup goals were all penalties scored by Mile Jedinak, who has now retired. Tim Cahill was the last Australian player to score from open play in the tournament, in 2014.
Australia have kept only one clean sheet in their 16 World Cup matches, that came 48 years ago with a goalless draw against Chile in the group stages of the 1974 edition.
Player prediction – Antoine Griezmann to provide an assist: Didier Deschamps might be without Ballon d'Or winner Karim Benzema, but since the 2014 World Cup, Cristiano Ronaldo is the only European player to have scored and assisted more goals (17) than Antoine Griezmann (15) at major tournaments. He should have the quality to provide at least one assist against Australia.
Match prediction – France will be made to wait: Each of France's last eight goals have been scored after half-time, last going on a longer run between October 1999 and April 2000 (10).