Juan Martin Del Potro is in action against Mardy Fish in the fourth round of the Miami Masters later today.

You can watch Del Potro v Fish live for free at bet365>livestreaming>tennis.

Del Potro looks like he's rapidly returning to the kind of form which saw him win the 2009 US Open. There were question marks over the Argentine's fitness after he required a hamstring to be strapped during an epic second round win over Philipp Kohlschreiber but he returned to the court with a vengeance on Sunday to destroy fourth seed Robin Soderling in straight sets.

Del Potro is the underdog on paper but recent form tells a very different story. The Argentine won the Delray Beach title last month and made the semi-finals of Indian Wells last week and appears to be showing no signs of tiring.

Fish went down to Milos Raonic in Indian Wells but the American has impressed in Miami, taking out Richard Gasquet in straight sets in the last round. Despite a poor serving performance, Fish played an intelligent match from the back of the court and won the battle of the backhands, a key aspect to defeating Gasquet.

"He's a great player," Del Potro said. "I'm a very good friend of him. He's a nice person, too. It will be a special match because I know him. He knows my game. We play many times against each other. And here in fourth round, every player is playing really well. So will be a nice match for both."   

The head-to-head between the two stands at 2-2 though Del Potro won the most recent encounter 6-1, 7-5 in Delray Beach last month.