Michael Phelps secured a gold medal in his final race as an Olympic athlete as the US won the 4x100m medley relay at the Rio Games.The US team of Ryan Murphy, Cody Miller, Phelps and Nathan Adrian clocked 3:27.95 to finish 1.29 seconds ahead of Britain's Chris Walker-Hebborn, Adam Peaty, James Guy and Duncan Scott on Saturday, reports Xinhua.Australia, represented by Mitchell Larkin, Jake Packard, David Morgan and Kyle Chalmers, took bronze in 3:29.93. Phelps began the butterfly leg with the USA in second position, but he set a blistering pace to give his team the lead by the end of his 100m.The victory gave Phelps his 23rd Olympic gold medal. The 31-year-old extended his record as the most successful Olympian in history with six medals - five gold and one silver -- at the Rio Games.