Played at an Al-Sadd Stadium packed with noisy expatriate Indians, a convincing win was needed by the Socceroos to demonstrate their tournament credentials against a team ranked 142 in the world. They comfortably delivered, with the dangerous Cahill, playing up front as the lone striker, a constant threat.
The Everton star got the opener in the 11th minute before Harry Kewell made it 2-0 14 minutes later. Brett Holman added a third on the stroke of half-time before Cahill completed the demolition in the second period.
Australia's positive start was in stark contrast the one they made four years ago at their maiden Asian Cup, when they stumbled to a draw with Oman before losing to eventual winners Iraq. The Australians squeezed through to the knock-out stages that year by thrashing Thailand 4-0, but went out on penalties to Japan in the quarters.
Coach Holger Osieck was happy with their performance. "It was very important to get a good start, to find our rhythm, to get a performance together," said the German. "From my point of view, it was a good game. We played technically very well in the first half. We scored four goals, which is very positive and encouraging. It should give us confidence for the next games to come."
Despite losing, India's English coach Bob Houghton applauded his young team. "We played a very good team today. It is not by fortune that Australia are number one in Asia," he said. "But our boys stuck to their task, we kept our shape and discipline. My players though will learn from this. No one likes to lose 4-0, but it was a good experience."
In breezy conditions, both sides began slowly with Australia getting the first sniff of goal on nine minutes when Holman looped the ball in to Blackburn's Brett Emerton, who fired straight at the goalkeeper. However, with a side packed by experienced Europe-based players, it was only a matter of time before the Socceroos got the breakthrough.
Emerton was put through on the right and he sent a low cross into the six-yard box, where Cahill was lurking to bury the ball in the back of the net. India, in the tournament for the first time in 27 years, were out of their depth but got a look at goal when captain Climax Lawrence's shot from 25 yards drifted well wide of the post soon after.
Australia could have been 2-0 up on 20 minutes when Cahill headed home but he was adjudged offside by UAE referee Ali Al Badwawi. They made amends just minutes later when Luke Wilkshire found Kewell in space just outside the penalty area and the Galatasaray midfielder clinically drilled the ball into the bottom left-hand corner.
With Fulham's Mark Schwarzer having nothing to do in the Australian goal, a third goal almost came on the half-hour with Cahill in the thick of the action again. India were struggling to contain him and he went close once again when he chested down a long ball and half-volleyed it just over the bar.
The third goal was inevitable and it came just before half-time when Holman got his head on the end of an Emerton cross after some good build-up work. Australia began the second-half in total control and Cahill got his second in the 65th minute when he outjumped four defenders to meet a Wilkshire cross and angle his header past the goalkeeper.
India, with Englishman Bob Houghton in charge, now have their work cut out with Group C clashes against mighty Korea Republic and a very capable Bahrain still awaiting them. Australia face the South Koreans on January 14 in a match that could determine who tops the group.