Robert Lewandowski scored his first World Cup goal as Poland earned a crucial victory over Saudi Arabia that leaves Group C wide open.
The Barcelona striker capitalised on an error by Saudi Arabia midfielder Abdelulelah Al Malki before sending a composed finish past onrushing goalkeeper Mohammed Al Owais.
Lewandowski, who missed a penalty in Tuesday's goalless draw with Mexico, was visibly emotional after ending a run of four World Cup games without finding the net.
Piotr Zielinski had given Poland a first-half lead from Lewandowski's cutback, but Saudi Arabia were awarded a penalty five minutes later for Krystian Bielik's foul on Saleh Al Shehri.
Wojciech Szczesny kept out Feras Al Brikan's effort before producing a sensational one-handed stop to prevent Mohammed Al Burayk from burying the rebound.
Saud Abdulhamid was denied by Sczcesny and Al Brikan shot over the bar in the second half, while Arkadiusz Milik and Lewandowski were both denied by the woodwork as Poland sought to double their lead on the counter-attack.
Lewandowski's late strike ended Saudi Arabia's hopes of building on Tuesday's remarkable victory over Argentina and boosts Poland's hopes of reaching the last 16 for the first time since 1986, when they were beaten 4-0 by Brazil in the first knockout round.
Czeslaw Michniewicz's team need just one point against Argentina on Wednesday to qualify from Group C, while Saudi Arabia face Mexico for a place in the last 16.
Wasteful Saudi Arabia rue missed opportunities
Lewandowski will steal the headlines after breaking his World Cup duck, but Saudi Arabia will be bitterly frustrated not to have preserved their unbeaten start to the tournament in Qatar after finding Sczcesny in inspired form.
Backed by a fervent and partisan crowd inside Education City Stadium, Saudi Arabia applied heavy early pressure and were denied a superb opener when the former Arsenal goalkeeper palmed Mohammed Kanno's ferocious drive over the crossbar.
Poland looked increasingly rattled as the Green Falcons continued to swarm forward in waves, but Bielik's goal-bound header was cleared to safety by Al Shehri before Zielinski gave them the lead with their first shot on target.
Bielik's challenge on Al Shehri shortly before half-time initially went unpunished by referee Wilton Sampaio, but the Brazilian showed no hesitation in pointing to the spot after reviewing the incident on his pitchside monitor.
If Szczesny's save from Al Brikan's spot-kick was impressive, his fingertip stop from Al Burayk's follow-up effort was spectacular - and will take some beating at this World Cup.
There was little change to the pattern of play in the second half, with Szczesny saving at the feet of Abdulhamid and Al Brikan sending a fierce, left-footed shot over the bar.
But Poland remained a threat on the counter-attack as Milik sent a powerful header against the crossbar, before Lewandowski's near-post flick also came back off the woodwork.
It was Al Malki's heavy touch that ultimately proved decisive, ending Saudi Arabia's hopes of becoming the first team in Qatar to clinch their place in the last 16.
Lewandowski could have doubled his tally in stoppage time, but Al Owais kept out the striker's effort with a strong hand.
Player of the match
CashMatty Cash
Poland
Squad number2Player nameCash
Squad number1Player nameSzczesny
Squad number9Player nameLewandowski
Squad number20Player nameZielinski
Squad number7Player nameMilik
Squad number18Player nameBereszynski
Squad number15Player nameGlik
Squad number6Player nameBielik
Squad number13Player nameKaminski
Squad number10Player nameKrychowiak
Squad number24Player nameFrankowski
Squad number14Player nameKiwior
Squad number23Player namePiatek
Saudi Arabia
Squad number21Player nameMohammed Al Owais
Squad number23Player nameMohammed Kanno
Squad number9Player nameFeras Al Brikan
Squad number6Player nameMohammed Al Burayk
Squad number4Player nameAbdulelah Al Amri
Squad number5Player nameAli Al Bulayhi
Squad number11Player nameSaleh Al Shehri
Squad number10Player nameSalem Al Dawsari
Squad number16Player nameSami Al Naji
Squad number8Player nameAbdulelah Al Malki
Squad number12Player nameSaud Abdulhamid
Squad number18Player nameNawaf Al Abid
Squad number24Player nameNasser Al Dawsari
Squad number19Player nameHattan Bahbri
Squad number20Player nameAbdulrahman Al Obud
Squad number2Player nameSultan Al Ghannam
Line-ups
Poland
Formation 4-4-2
1Szczesny
2Cash14Kiwior15Glik18Bereszynski
20Zielinski6Bielik10Krychowiak24Frankowski
7Milik9Lewandowski
1Szczesny2CashBooked at 16mins14KiwiorBooked at 15mins15Glik18Bereszynski20ZielinskiSubstituted forKaminskiat 63'minutes6Bielik10Krychowiak24Frankowski7MilikBooked at 19minsSubstituted forPiatekat 71'minutes9LewandowskiSubstitutes
3Jedrzejczyk4Wieteska5Bednarek8Szymanski11Grosicki12Skorupski13Kaminski16Swiderski17Zurkowski19Szymanski21Zalewski22Grabara23Piatek25Gumny26SkórasSaudi Arabia
Formation 4-1-4-1
21Al Owais
12Abdulhamid4Al Amri5Al Bulayhi6Al Burayk
8Al Wahbi Al Malki
9Al Brikan16Al Naji23Kanno10Al Dawsari
11Al Shehri
21Al Owais12Abdulhamid4Al AmriBooked at 45mins5Al Bulayhi6Al BuraykSubstituted forAl Ghannamat 65'minutes8Al Wahbi Al MalkiBooked at 21minsSubstituted forAl Obudat 85'minutes9Al Brikan16Al NajiSubstituted forAl Abidat 45'minutesSubstituted forBahbriat 90+5'minutes23Kanno10Al Dawsari11Al ShehriSubstituted forAl Shardan Al Dawsariat 86'minutesSubstitutes
1Al Rubaie Al Yami2Al Ghannam3Madu14Otayf15Al Hassan17Al Tambakti18Al Abid19Bahbri20Al Obud22Al Suweiti Al Aqidi24Al Shardan Al Dawsari25AsiriReferee:Wilton Pereira SampaioAttendance:44,259Live Text
Match ends, Poland 2, Saudi Arabia 0.
Second Half ends, Poland 2, Saudi Arabia 0.
Attempt missed. Mohammed Kanno (Saudi Arabia) right footed shot from outside the box is close, but misses to the right. Assisted by Salem Al Dawsari.
Substitution, Saudi Arabia. Hattan Bahbri replaces Nawaf Al Abid.
Corner, Poland. Conceded by Abdulrahman Al Obud.
Corner, Poland. Conceded by Sultan Al Ghannam.
Attempt saved. Robert Lewandowski (Poland) right footed shot from the right side of the box is saved in the centre of the goal.
Foul by Nasser Al Dawsari (Saudi Arabia).
Krzysztof Piatek (Poland) wins a free kick in the defensive half.
Attempt missed. Abdulrahman Al Obud (Saudi Arabia) header from the right side of the six yard box is just a bit too high. Assisted by Nasser Al Dawsari with a cross.
Substitution, Saudi Arabia. Nasser Al Dawsari replaces Saleh Al Shehri.
Substitution, Saudi Arabia. Abdulrahman Al Obud replaces Abdulelah Al Malki.
Abdulelah Al Malki (Saudi Arabia) wins a free kick in the defensive half.
Foul by Jakub Kaminski (Poland).
Goal! Poland 2, Saudi Arabia 0. Robert Lewandowski (Poland) left footed shot from the centre of the box to the centre of the goal.
Attempt missed. Krzysztof Piatek (Poland) header from the centre of the box is high and wide to the left. Assisted by Jakub Kaminski with a cross.
Foul by Feras Al Brikan (Saudi Arabia).
Bartosz Bereszynski (Poland) wins a free kick on the left wing.
Attempt missed. Abdulelah Al Malki (Saudi Arabia) left footed shot from the centre of the box is close, but misses to the right.
Foul by Sultan Al Ghannam (Saudi Arabia).
Get the latest results and goal notifications for any team at the Fifa World Cup by downloading the BBC Sport app: Appleexternal-link - Androidexternal-link - Amazonexternal-link
Get your daily dose of Fifa World Cup reaction, debate & analysis with World Cup Daily on BBC Sounds