South Korea swept past already-eliminated India 4-1 to set up a last eight meeting with three-times champions Iran, meaning a fifth consecutive Asian Cup quarter-final between the teams.
"Iran is one of the powerhouses of Asian football and, in order to win the tournament, we have to beat them. That's it," Korean coach Cho Kwang-rae told reporters.
The Koreans, however, may regret the number of chances they missed at a rain-soaked Al Gharafa Stadium as one more goal would have meant they topped Group C and set up a meeting with either holders Iraq, United Arab Emirates or North Korea who have all looked far less dangerous than Iran.
However, Australia will meet whichever of the three finishes as Group D runners-up after they edged a dogged Bahrain 1-0 at a wet and windy Al Sadd Stadium to top the group on goal difference.
Bahrain finished third with three points and India, playing in their first Asian Cup since 1984, bottom with none.
The Socceroos were not at their best but defended well and managed the difficult conditions better to restrict their opponents, who needed to win to advance, to long range efforts.
"It was a tough game and Bahrain... gave us a hard time. We won tough. We topped the group which is positive for the morale for the next coming games," Australia coach Holder Osieck told reporters.
Australia took the lead in the 37th minute after an even opening when midfielder Mile Jedinak collected a clearance and smashed a low, bouncing right-foot shot from 25 metres past Mahmood Mansoor in the Bahrain goal.
It was the second goal of the tournament for Jedinak, which came shortly after Bahrain striker Ismaeel Abdulatiff, who scored four in a 5-2 win over India last time out, hit the outside of the post from an acute angle.
South Korea, seeking their first Asian title since 1960, impressed in their opening two matches in Doha and were expected to easily beat India, the lowest ranked in the 16-team tournament.
Ji Dong-won put the Koreans ahead after just six minutes and Koo Ja-cheol doubled the advantage three minutes later with his fourth goal of the tournament when he rounded the keeper to score from close range.
Indian striker Sunil Chhetri replied with a 12th minute penalty but the Koreans struck right back with Ji's second of the game in the 23rd minute.
Korea dominated the second half and could have scored at least three more, but had to settle for four with 18-year-old substitute Son Heung-min smashing home a left-foot shot nine minutes from the end after a superb through ball from Ja-cheol.
"We failed to convert a lot of chances, but I am pleased with the attitude of the players. They took the game very seriously," Cho said of his team who had 38 attempts at the Indian goal.
Indian striker Bhaichung Bhatia, the country's most famous player, came on for the last 12 minutes after nursing a year-long calf injury to record probably his last appearance for the Bhangra Boys after winning more than 100 caps.
