Argentine, Juan Martin Del Potro has produced the biggest upset of the Rio Olympics, knocking out world No.1 Novak Djokovic in the first round of tennis.

Del Potro prepared for his Olympics opener against Djokovic trapped inside an athlete's village elevator for 40 minutes yesterday, with no reception to communicate with the outside world.

He was eventually rescued by the Argentinian handball team, later going on to defeat Djokovic in an epic battle 7‑6, 7‑6.

Del Potro turned back the clock in front of a vocal crowd in the Olympic Tennis Centre, getting the better of the Serbian in a tie break to claim a fascinating first set win and repeating his heroics in the second to win the match.

In swimming, Michael Phelps helped the USA 4 by 100m freestyle team to win gold in the last hour.