Senegal moved into the 4/5 favourites to win Group H after they secured a 2-1 victory over Poland in Moscow.
Poland, the backed team pre-tournament for Group H success, now find themselves as the 11/1 outsiders, with 5/2 available on qualification to the Round of 16.
Playing in their first match on this stage since their memorable run to the quarter-finals in 2002, Senegal triumphed thanks to two goals that owed much to Polish generosity: a Thiago Cionek own goal and a horrible mix-up to let in Mbaye Niang for a tap-in.
A meaty Grzegorz Krychowiak header late on gave Poland a chance of a draw but they did not really deserve it and Senegal comfortably closed out the game.
The contest had been set up as a battle between two players who occupy the tier of talent just below the holy trinity of Messi, Neymar and Ronaldo: Poland's captain and talisman Robert Lewandowski and Senegal's main man, Sadio Mane.
In Monday's pre-match press conference, Senegal coach Aliou Cisse bristled at the suggestion the Liverpool star was not already considered one of the world's best and on Tuesday he helped underline the man-on-Mane narrative by dropping his captain, West Ham's Cheikhou Kouyate, and giving the armband to his superstar.
Poland's line-up drama boiled down to one story - would their towering centre-back Kamil Glik be fit after injuring himself practising an overhead kick? The answer was no, which meant a start for Cionek. The significance of this would grow.
The match started against a backdrop of red and white flags, shirts and painted cheeks, as Polish fans outnumbered Senegal's by about 20 to one. Having belted out their own anthem, the Poles sportingly applauded Senegal's "Pincez tous vos koras, frappez les balafons", or "Strum your koras, bang the balafons".
If the Polish did not know what a kora or balafon was, they soon found out, because Senegal's support was basically two bands: a gently swaying group with percussion on one side of the pitch, and a high-energy dance troupe with koras, balafons and the kitchen sink on the other.
It was the sort of match where such distractions were welcome.
Poland had most of the ball but went witlessly from side to side until they lost it. Senegal would then charge forward only to run out of pitch.
Well-marshalled by Senegal's imposing central defenders, Lewandowski could not get a sniff, while Mane spent the first 25 minutes on the left touchline, just where Poland wanted him.
The opening goal was in keeping with everything the crowd had seen for the first 37 minutes but for one subtle difference: Mane had moved inside. So when another Polish attack broke down, he received the ball in space directly in front of a back-pedalling defence.
They clearly did view him as one of the world's best as they let him take two touches and calmly roll the ball to Everton's Idrissa Gueye, who then scuffed a 25-yard shot.
It would have gone wide if Cionek had not decided to wrong-foot former Arsenal goalkeeper Wojciech Szczesny and plant it in the bottom corner of his net. Senegal's bands went ballistic.
This, however, was not a shot on target and the teams did not register one until Lewandowski took matters into his own hands after the break by winning a tackle, beating his man and then earning a free-kick in front of goal. His shot was theatrically saved by Khadim Ndiaye.
But worse was to come for Poland on the hour. Much worse.
With another Polish move breaking down, Krychowiak, who did not cover himself in glory while on loan at West Brom last season, looped a back-pass in the general direction of Southampton's Jan Bednarek, just on as a substitute.
What neither he nor the dawdling Bednarek spotted was that Niang had just been waved back on the pitch by the referee after some treatment.
Szczesny spotted it, though, and came racing out of his goal to save the day. Sadly for Poland, he was a split second late, allowing Niang to dink it past him and tap into an empty net. This, obviously, was Senegal's first shot on target.
Poland kept huffing and puffing and they and Krychowiak gained some consolation when he planted a firm header past Ndiaye with four minutes to play. Having checked to see he was onside - he was, just - the Bahraini official blew his whistle and the majority of the Spartak Stadium came alive again.
It was too little, too late, though, and the beat from the Senegalese drums never dipped. This was their day and Africa is finally on the board in Russia.
GOAL! Senegal take the lead after Gana's shot takes a big deflection off Cionek.#WorldCup #POLSEN pic.twitter.com/XJxJ2ECWxb
— ITV Football (@itvfootball) June 19, 2018
Senegal double their lead thanks to Niang's opportunistic interception!#WorldCup #POLSEN #SEN pic.twitter.com/WOi7YL34Cv
— ITV Football (@itvfootball) June 19, 2018
Krychowiak pulls one back for Poland#WorldCup #POLSEN #POL pic.twitter.com/WeuDjP02Em
— ITV Football (@itvfootball) June 19, 2018
To follow shortly...
Odds correct as of 1805 BST 19/06/18