The Australian coaches rested O'Brien for the heats of the 4 × 100 m medley relay; Peter Tonkin swam the breaststroke leg instead. It turned out to be a close call for the Australians, as they finished fourth in their heat and qualified seventh fastest, only 1.2 s from elimination. In the final, O'Brien was brought into the team to combine with Peter Reynolds, Berry and Dickson. At the end of Reynolds' backstroke leg, Australia were sixth, 3.4 s behind the American leaders. O'Brien dived in and completed his leg in 1 min 7.8 s, a breaststroke split bettered by only Henninger and Prokopenko. This pulled Australia up to fourth position, 1.7 s in arrears of the Americans at the halfway mark. Australia progressed further to finish third behind the United States and Germany in a time of 4 min 2.3 s, missing the silver by 0.7 s.