Senegal upset Poland with a 2-1 Group H victory in Moscow that owed plenty to poor mistakes from the European nation.
Poland were widely expected to qualify for the knockout rounds but after suffering a seventh loss in their last nine World Cup matches, FIFA's eighth-ranked team are in danger of making an early exit.
Thiago Cionek's own goal, the defender deflecting in a shot from Idrissa Gueye, handed Senegal the lead in the 37th minute.
Senegal doubled their lead when M'Baye Niang took advantage of a mix-up between Grzegorz Krychowiak and Wojciech Szczesny to finish with ease.
Adam Nawalka's side set up an exciting finish when Krychowiak somewhat made amends for his error by heading home a Kamil Grosicki free-kick, but they could not find a late leveller.
Poland will need to make amends when they take on Colombia - who surprisingly lost to Japan on Tuesday - while Senegal have qualification for the next phase in their sights.
A slow start at Spartak Stadium saw neither side gain control of the midfield until Senegal had the first clear chance in the 18th minute, Niang dragging a poor effort wide after a break.
The African side - who shocked France on their World Cup bow in 2002, their only previous appearance - gradually started to dominate but the opening goal had a large slice of good fortune.
Patient passing produced an opportunity for Gueye, albeit his 20-yard strike took a huge deflection off Cionek to wrong-foot Poland goalkeeper Szczesny.
Nawalka sent on Southampton defender Jan Bednarek at half-time - Jakub Blaszczykowski making way on his 100th international appearance - as Cionek's own goal ensured Poland's 32-year wait for a clean sheet at the World Cup goes on.
Poland captain Robert Lewandowski was Europe's top scorer in qualifying with 16 goals but when he stepped up to float a 25-yard free-kick over the wall, Khadim N'Diaye acrobatically dived to turn the ball away.
A much-improved Poland continued to threaten and Lukasz Piszczek should have hit the target with a volley at the back post from a deep right-wing centre from Maciej Rybus.
But while the Senegal first was unlucky for Poland, they were architects of their own downfall for the decisive second, handing Niang his first international goal on the hour mark.
Krychowiak needlessly hooked a high ball back towards his own goal from inside the Senegal half and with Szczesny attempting to intercept by coming out of his penalty area, Niang gleefully knocked the ball into an unguarded goal.
Arkadiusz Milik should have got Poland back in the game but he slotted a perfect Piszczek cross wide at the near post.
Dawid Kownacki's headed attempt was easily saved late on by N'Diaye but the goalkeeper was beaten by Krychowiak's well-placed header with five minutes to go.
Yet Senegal held on to their advantage in a nervy finish, leaving the Euro 2016 quarter-finalists with plenty to do if they are to qualify from a suddenly wide-open group.
Key Opta Stats:
- Senegal have won 50 per cent of their World Cup matches (3/6), the best win rate of any African nation.
- Poland have failed to keep a clean sheet in each of their last nine World Cup matches, since beating Portugal 1-0 in 1986.
- Grzegorz Krychowiak scored Poland’s first goal at a World Cup since 2006, when Bartosz Bosacki scored twice against Costa Rica.
- Thiago Cionek’s own goal was the only second time an African nation has benefited from an own goal in a World Cup match, after Andoni Zubizarreta for Spain against Nigeria in 1998.
- M’Baye Niang’s goal was his first ever for Senegal, scored with his first shot on target in a World Cup match.
|Paul hails ´sick´ Harden after record-breaking display|
|Liverpool v Manchester United: Salah, Mane and Firmino v Rashford, Martial and Lukaku in Opta number|
|Canelo open to GGG trilogy as he chases place in Mexican history|
|The big Friday Premier League quiz|
|Harden posts record fourth 50-point triple-double in win over Lakers|
|Barcelona squad happy with Dembele, says Alba|
|Chargers rally past Chiefs to clinch playoff spot|
|WATCH: Chargers top Chiefs on dramatic two-point conversion in final seconds|
|Suns owner Sarver committed to keeping team in Phoenix|
|Chargers WR Allen leaves with injury after near-spectacular catch|
|Socceroos not giving up on Mooy for Asian Cup|
|Cooper says Raiders owner wanted to trade him to Cowboys|
|Pochettino jokes Levy is ´worried´ about losing him|
|Barcelona would welcome Morata – Alba|
|Toure not a priority for West Ham – Pellegrini|
|Koscielny no certainty to face Southampton, says Emery|
|We gifted the game – AC Milan boss Gattuso furious after Europa League exit|
|My season starts now, says Koscielny|
|Cipriani ´at peace´ with latest England snub|
|Laporte: Deschamps must have personal reasons for France snub|
|Morata injury not too serious, claims Chelsea boss Sarri|
|Hansen to leave: All Blacks coach returning focus to World Cup defence|
|I want to fight the champion! - Joshua reiterates Wilder in April ambition|
|Gundogan glad to leave Christmas holidays behind|
|I know how it feels and it hurts - Gundogan on Sterling abuse|
|Celtic 1 Red Bull Salzburg 2: Scottish champions through despite defeat|
|Olympiacos 3 AC Milan 1: Rossoneri crash out of Europa League|
|Arsenal 1 Qarabag 0: Lacazette on target as Saka shines|
|Hansen to leave: All Blacks will take time to name replacement|
|Chelsea condemn alleged anti-Semitic chanting from fans|
|Hansen to leave: The best Opta facts from New Zealand coach´s tenure|
|Hansen to leave: Five contenders to be the next All Blacks coach|
|Hansen to leave: Highs and highs of his All Blacks reign|
|Hansen to leave All Blacks after World Cup|
|Rapid Vienna 1 Rangers 0: Late Ljubicic winner sends Gerrard´s men out|
|Beckham continues to miss Giants practice with quad injury|
|Vidi 2 Chelsea 2: Giroud spares Sarri´s side in lacklustre draw|
|Paris Saint-Germain and Marseille fixtures among latest Ligue 1 cancellations|
|Santos turn to ex-Argentina boss Sampaoli|
|Muller could miss Champions League last 16 after Tagliafico kick|
|Home hope Bekker out in front at Alfred Dunhill Championship|
|Van Bommel in touch with Robben over PSV reunion|
|Pinarello chief confident over Team Sky future|
|Stade make Ospreys tickets free in tribute to teenager|
|WRC great Loeb seals Hyundai switch|
|Madrid rumours better than sack talk, says Pochettino|
|Nadal to join Federer at 2019 Laver Cup|
|Prigoda smashes world record, Hosszu dethroned in Hangzhou|
|Former Juve CEO Marotta takes over at Inter|
|Glenn to stand down as FA boss next year|
|Muller apologises to Tagliafico for kick to the head|
|Pereira pleads for more Manchester United chances|
|Griffin hails ´phenomenal´ Lowry after Warriors demolition|
|I´ve played with Zidane and Henry, but Messi is something else – Pires|
|Dragons forward Jack de Belin charged with sexual assault|
|Durant: Raptors are the real deal|
|Cocu bids farewell to Fenerbahce after ´mutual agreement´ is made over October sacking|
|Australia unchanged for historic Perth Test|
|Champions League draw: The possible last-16 ties|
|Southee happy to be back on home soil|
|I wouldn´t swap Dembele for Neymar – Pires|
|Canelo ready to risk heavy weather against Fielding|
|Raptors upstage Warriors, Davis leads Pelicans with 44 points|
|India skipper Kohli excited by green Perth wicket|
|PSG? I haven´t decided my future yet – De Jong|
|Marcelo: Real Madrid don´t have attitude problem|
|India pair Ashwin, Rohit ruled out of second Test|
|Kovac: Ajax-Bayern draw was amazing|
|Sims re-signs with Dragons until 2022|
|Derrius Guice injury update: Redskins RB (knee) has rehab setback, undergoes 3 more procedures|