The narrow triumph for Phelps, Ryan Lochte, Peter Vanderkaay and Klete Keller - in an American record of 7min 07.33sec - gave Phelps his second gold medal of the night after his victory in the 200m butterfly.

It was a triumphant day for the South Asian giants India and Pakistan in men's hockey. The two former world-beaters came back strongly from opening day defeats with wins over South Africa and Egypt respectively.

There was a stunning upset in men's tennis as world number one Roger Federer of Switzerland crashed out of the Games.

The day was also blackened by drugs controversy. World 100 metres champion Torri Edwards lost her appeal to be reinstated to the US Olympic team after the Court of Arbitration for Sport (CAS) rejected her appeal against a two-year drugs ban.

But swimming overshadowed every other event with Phelps starring.

In the 4x200m, he got the Americans off to a flying start, but it was anchor swimmer Keller who held off Thorpe - just a day after the mighty Australian underscored his hold on the event by winning the individual 200m free title. The Aussies settled for silver in 7:07.46.

Italy took third in 7:11.83.

Nineteen-year-old Phelps had added the 200m butterfly gold to his 400m individual medley title at the Games earlier on Tuesday.

Phelps was nearly half a second under his world record pace through 100m, winning in an Olympic record of 1min 54.04sec.

Tennis ace Federer lost to unseeded Tomas Berdych of the Czech Republic.

The Czech, ranked 74 in the world, beat the Australian Open and Wimbledon champion 4-6, 7-5, 7-5 in the second round and now plays Spain's 15th seed, Tommy Robredo.

In hockey, India scored twice in the last two minutes to record a remarkable 4-2 win over South Africa in group B.

The former champions were down on the count when Greg Nicol and Craig Fulton put South Africa 2-0 ahead in the first 12 minutes.

India, stung by the early reverses, regrouped quickly and were rewarded with two score-levelling goals either side of the interval through veterans Dhanraj Pillay and Baljit Dhillon.

The match appeared headed for a draw when captain Dilip Tirkey netted a penalty corner in the 69th minute and Gagan Ajit Singh found the target just before the final whistle for India.

Meanwhile, prolific scorer Sohail Abbas netted four goals, including a penalty stroke, as Pakistan thrashed unfancied Egypt 7-0 in the Olympic men's field hockey here on yesterday.