Murray, 34, a two-time winner, will play Russian Medvedev, who lost the world number one ranking on Monday.

Medvedev spent three weeks at number one and must reach the semi-finals in Miami to again replace Serb Novak Djokovic at the top of the men's game.

Murray won four consecutive points to edge an even opening set in a tie-break at Hard Rock Stadium - but he made lighter work of the second set, breaking the Delbonis serve for 1-0 and 4-1 leads before another sealed the victory.

Three-time Grand Slam winner Murray has not won back-to-back matches since the Sydney Classic in January, exiting in the second round at Indian Wells last week.

Medvedev, 26, received a bye in the first round in Miami. He has said he wants to continue promoting his sport, but that he is not sure if he will be allowed to play on amid Russia's invasion of Ukraine.

Players from Russia and Belarus are not allowed to compete under their own flag but at present they can compete as individuals.