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.
|Richarlison: I want to be at the Copa America|
|Tabarez buoyed by inexperienced Uruguay|
|Howell fires 64 again to extend RSM Classic lead|
|I´m proud of them - Giggs still upbeat despite Denmark defeat|
|Mancini ´very sorry´ for Ronaldo absence|
|Neymar clinches anything-but-friendly win for Brazil over Uruguay|
|Cipriani-inspired Gloucester thrash Tigers|
|Djokovic makes it three wins from three at ATP Finals|
|Germany relegated from Nations League top tier to cap miserable 2018|
|Fulham will back Ranieri in January transfer window if required|
|Brazil 1 Uruguay 0: Neymar penalty settles tight contest|
|Netherlands 2 France 0: Wijnaldum & Depay decisive as Germany are relegated|
|Wales 1 Denmark 2: Jorgensen and Braithwaite seal Nations League promotion|
|Oxlade-Chamberlain targeting early return|
|New Zealand-born Aki will ´relish´ facing All Blacks – Marmion|
|Portugal cannot focus on absent Ronaldo - Santos|
|Ramsey reiterates he wants to stay with Jaguars despite cryptic tweet|
|We tried to hit a home run and it didn´t work out - D´Antoni explains Carmelo exit|
|West Ham´s Zabaleta backs Premier League´s VAR introduction|
|Southgate eyes winning end to England´s ´brilliant year´|
|Patient Zverev seizes opportunity to make amends at ATP Finals|
|Rodgers: Packers still believe they can make playoffs|
|Mahomes hoping to ketchup to Heinz´s touchdown target|
|Ranieri tells Fulham fans not to expect repeat of Leicester ´fairytale´|
|Brown to leave role as RFU chief executive|
|Croatia star Rakitic ruled out of England clash|
|Capital gains for Zverev as he secures last-four spot in London|
|Sancho rise continues with Player of the Month award|
|Jones-Buchanan, Ablett and Briscoe sign new Rhinos deals|
|Root leads from the front as aggressive England assume control|
|Croatia´s Lovren antagonises Ramos and ´rude´ Spain|
|Rakitic has ´enormous respect´ for England ahead of Nations League decider|
|Ireland make flanker switch with Leavy out of All Blacks clash|
|Pakistan rip through Black Caps in Abu Dhabi|
|WATCH: Barcelona mark 15-year anniversary of Messi´s first match|
|Sterling, that you? - Walker uses falling fan to poke fun at England team-mate|
|Fleetwood applies pressure on Molinari, Wallace leads in Dubai|
|Don´t talk to me about VAR – Rakitic not over World Cup final loss|
|Van Dijk leadership essential for Liverpool – Wijnaldum|
|Dalic: Croatia´s bench was ready to stop Spain!|
|Sublime Root century gives England imposing lead|
|Vinicius appreciates Solari influence at Real Madrid|
|Havertz would suit Bayern Munich – Kimmich|
|Wilder: Roach recruitment a sign of Fury nerves|
|Ranieri targets defensive improvements at failing Fulham|
|PSG close investigation into player recruitment practices after finding no discrimination|
|Mayweather: Nasukawa exhibition back on|
|Witsel: Joining Borussia Dortmund my best career decision|
|Ballon d´Or win would not change Modric´s ´best year´|
|Ireland v New Zealand: Opta stats behind the meeting of the world´s top two|
|The Breakdown: A statistical look at Saturday´s rugby internationals|
|Batshuayi dismisses reports of Valencia departure|
|Brazil must make Copa America final – Tite|
|Rockets rout Warriors as Green goes scoreless|
|Seahawks rally past Packers|
|Lakers G Rondo to miss 4-5 weeks|
|Durant is done with questions about Green|
|Smith, Warner set to return to IPL in 2019|
|No rivalry between Mbappe and Griezmann – Deschamps|
|Neymar: Emery will bring success to Arsenal|
|Jedvaj backs Croatia to deliver against England|
|Howell grabs first-round lead at Sea Island|
|Rooney backing Kane to break England record|
|Betts named American League MVP|
|Republic of Ireland must improve, says under-pressure O´Neill|
|Injured Sergio Ramos to leave Spain squad|
|Yelich named National League MVP|
|Low praises ´beautiful goals´ from Sane and Gnabry|
|Belgium boss Martinez pleased with patient Batshuayi|
|Wilson and Sancho pay tribute to England ´legend´ Rooney|