K-League newcomers Sangju Sangmu held Jeonbuk Motors to a goalless draw on Sunday as the two-time champions lost top spot.
Hosts Sangju kept up their solid, if unremarkable, start to life in the top flight with a third successive draw, overcoming the 58th-minute dismissal of Lee Jae-Seong to end Jeonbuk's perfect start to the campaign.
Jeonbuk's weekend was made worse when Ulsan claimed a third win from three in Sunday's final game with a 3-0 triumph over Incheon United.
Kim Shin-Wook continued his record of scoring in every round of games this season, finding the net after just five minutes at the Munsu Cup Stadium.
Han Sang-Woon made it 2-0 14 minutes later before Incheon's Choi Jang-Hwan was shown a red card.
Rafinha wrapped up the scoring and the points just before the hour, with Ulsan now the only side in the division to boast a 100 per cent record.
Jeonnam Dragons, Jeju United and Busan I'Park all sit three points behind the leaders after registering victories over the weekend.
The Dragons showed their fighting qualities in a 3-2 triumph over Gyeongnam, having found themselves a goal down after half an hour.
Ahn Yong-Woo and Stevica Ristic turned the game on its head only for Milos Stojanovic to level shortly after the interval.
Lee Jong-Hoo then claimed the crucial winner to help his side bounce back from defeat to Jeju United last time out.
Jeju beat Seongnam 1-0, with Song Jin-Hyung on target 18 minutes from time, while Busan claimed a narrow 1-0 win at Seoul.
Yang Dong-Hyun got the all-important goal for the visitors, who finished with 10 men due to Lee Won-Young's late dismissal.
Reigning champions Pohang Steelers are up to eighth after coming from behind to defeat 10-man Suwon Bluewings and record their first win of the season.
Ko Cha-Won opened the scoring five minutes in and Pohang had to wait until seven minutes after the hour mark to level through Moon Chang-Jin, with the equaliser coming soon after Cho Ji-Hoon had seen red.
Ryu Chang-Hyun then popped up with a last-minute winner to get the holders' season up and running at the third time of asking.
|Coach: Hang-Seo Park|
for Hu-Kwon Lee 46'
for Jung-Hyub Lee 55'
for Jae-Sung Ko 75'
|Gerrard, Keane and Bradley pull out of MLS All-Star squad|
|Marseille reach Diaby agreement|
|Sammer thrilled with Vidal´s winning mentality|
|Platini expected to launch FIFA presidency bid|
|Romanov sacked me over Barca snub - Korobochka|
|Villa complete Crespo capture|
|Wolfsberger v Borussia Dortmund: Bender praises ´fun but exhausting´ training|
|Okaka swaps Sampdoria for Anderlecht|
|Southampton v Vitesse: Fonte excited for ´dream´ sojourn into Europe|
|Bournemouth agree King compensation|
|West Ham v Astra: Kouyate confident West Ham can progress|
|Vidal completes Bayern switch, signs four-year deal|
|Fabregas calls for Champions League improvement|
|BREAKING NEWS: Filipe Luis completes Atletico return|
|Bayern to present Vidal|
|Wenger unfazed by Mourinho´s spending jibe|
|Pellegrini: Sterling will justify price tag|
|Cavani hit with two-match Uruguay ban|
|Bonucci to remain at Juve until 2020|
|No bids for Berahino - West Brom|
|Putin: Blatter deserves a Nobel prize|
|Howe: Swansea a benchmark for Bournemouth|
|New Parma to play in Serie D|
|Mata vows to hit the goal trail at United|
|Drogba ´perfect fit´ for Montreal|
|Berahino ´not yet´ ready for Tottenham - Irvine|
|Romero lauds caring Van Gaal|
|Jese flying at Real under Rafa|
|Sampdoria unwilling to pay €10m for Balotelli|
|Mourinho talks up Arsenal title chances|
|Hull sign Ryan Taylor, Sam Clucas|
|Kane, Pochettino hail MLS All-Star test|
|Di Santo sorry for swift Werder departure|
|Mourinho tells Ronaldo: Team honours come first|
|Khedira returns to Juve training|
|Celtic v Qarabag: Champions League return of utmost importance, says Collins|
|Pellegrini: Jovetic had to go|
|Manquillo completes Marseille move|
|Schalke reject Juve´s Draxler bid|
|Blanc: Di Maria deal ´close´|
|Di Santo debut ends in stalemate|
|Fire sign Drogba, trade him to Montreal Impact|
|FIFA and UEFA welcome ruling on third-party ownership|
|Juve kick off title defence against Udinese|
|Stoke sign free agent Afellay|
|Benitez confident Ramos will stay|
|Fenerbahce issue warning to fans|
|UEFA Champions League Preview: De Boer confident Ajax are ready for Vienna test|
|Bility: I am the favourite for FIFA presidency|
|Pienaar to miss start of season|
|Vietnam 1 Manchester City 8: Sterling shines as tourists run riot|
|All-Star Keane relishing Spurs clash|
|Shaun Wright-Phillips joins brother Bradley at Red Bulls|
|Inter 0 Real Madrid 3: Rodriguez stunner caps comfortable win|
|Villa sign Ayew|
|Watford complete Berghuis transfer|
|Robben returns to Bayern training|
|Pulis anxious to make West Brom additions|
|David Luiz eager to welcome ´fantastic´ Di Maria|
|Fernando injury free ahead of new campaign|
|Hummels blames weight issues for poor season|
|Defoe hoping for early Sunderland goals|
|Depay hints at identity of ´surprise´ United striker|
|Tigres UANL v River Plate: Hosts look to bounce back and make history|
|Crespo set for Villa move|
|Terry: I would never join a Premier League rival|
|Van Gaal coy on United future|
|Romero to cover potential De Gea exit - Van Gaal|
|Uruguay win men´s football gold at Pan Am Games|
|Pirlo thanks New York City fans for ´beautiful´ welcome|
|Mexico capitalised on ´the mistakes we made´ - Schafer|
|Herrera delighted with Mexico display|
|MLS Review: Whitecaps build happy home, Pirlo debuts|
|Guardado wins Golden Ball at Gold Cup|
|NZF confirms Olympics disqualification appeal|
|Jamaica 1 Mexico 3: CONCACAF giants complete form turnaround|
|New York Red Bulls 2 Benfica 1: Another scalp for MLS side|
|Romero signs with United|
|Moghreb Tetouan 1 Al Hilal Omdurman 1: Visitors go top|
|Van Gaal rules out Ronaldo bid|
|Pique open to Barca captaincy|
|Pirlo makes MLS bow in thrilling NYC victory|
|Coutinho and Can return for Liverpool U21s|
|Walcott deal ´closer´, says Wenger|
|Arsenal 1 Wolfsburg 0: Walcott the match-winner in Emirates Cup finale|
|Di Santo links up with Schalke squad|
|Lukaku treble sinks Hearts|
|Benitez again refutes Ronaldo rift rumours|
|Pepe sure Ramos will stay at Real|
|City target De Bruyne named Germany´s Player of the Year|
|Montero spoils McCarthy´s Palace debut|
|Lyon 0 Villarreal 2: Soriano, Baptistao seal comfortable win in Emirates Cup|
|Wijnaldum on target as Newcastle are held|
|Mourinho: Rivals trying to buy the title|
|Jovetic set for Inter medical|
|RFS in ´denial´ over racism issue, claims Football Against Racism in Europe|
|Salah not staying at Chelsea - Mourinho|
|Mbemba closes in on Newcastle switch|
|Ibrahimovic: Di Maria will take PSG to another level|
|Delph: Don´t compare me to Pogba|
|Dundee United sign Sneijder|
|Morata relishing new-look Juve strikeforce|
|Strachan "not scared" of England after World Cup qualifying draw|
|Brazil claim football, basketball, handball gold in Toronto|
|Lampard´s debut delayed again, Pirlo ready to play|
|Mourinho open to Premier League matches in US|
|MLS Review: Texas unites to hurt Galaxy|
|Luis Enrique: United can emulate Barca revival|
|Van Gaal singles out Januzaj, hails United´s forwards|
|Blanc still hopeful PSG will sign Di Maria|
|Irish international Cunningham seeks Bristol City exit|
|Italy embracing Spain challenge in World Cup qualifying|
|Dos Santos brothers in doubt for Gold Cup final|
|PSG 1 Chelsea 1 (aet, 5-6 on penalties): Courtois clinches victory for Mourinho´s men|
|United States 1 Panama 1 (aet, 2-3 on penalties): Mejia denies hosts third|
|ES Setif 1 Al Merreikh 1: Sudanese deny title-holders at home|
|CONCACAF admit referee errors in Gold Cup semi-final|
|Dutch favourites in Group A - Deschamps|
|Barcelona 1 Manchester United 3: Rooney, Lingard and Januzaj maintain winning start|