After a marathon battle, Andy Murray finally felled Juan Martin del Potro in a gruelling four sets to win his second Olympic men's singles gold medal at Rio 2016.

An absorbing match lasting four hours and two minutes - ending with both players in tears - saw Murray triumph 7-5 4-6 6-2 7-5 to become the first player in history to win two singles golds and defend an Olympic singles title.

"I know tonight's one of the hardest matches that I've had to play for a big, big title," said Murray after the emotional and physical rollercoaster. "I think, you know, the US Open final I played against Novak [Djokovic] when I won my first slam was very hard. But tonight I found really difficult.

"Emotionally it was tough," he continued. "Physically, it was hard. There were so many ups and downs in the match. It was one of the toughest matches that I've played to win a big event, for sure."

Murray took the opening set but, as he had done in his third round and quarterfinal matches at Rio de Janeiro's Barra Tennis Centre, handed over the second in the face of some characteristically huge hitting from Del Potro.

The world No. 2 seized back the initiative in the third, seemingly getting a handle on Del Potro's fierce forehand, but Del Potro, despite appearing to be on his last legs between points, somehow found a third, fourth and even fifth wind.

After a muscle rub from the physio at 3-2 in the fourth game and apparently running on his last reserves, he was soon back in his stride to steal a break in the seventh.

Just when Del Potro appeared destined to force a deciding fifth set, he was pinned back on the ropes at 15-40 and, while the Argentine saved several break points, Murray won two stunning points at deuce and followed with a masterclass in counter-punching to stay alive in the set.

Murray had to fight back from 15-40 down on his own serve in the very next game but held, and he was soon rewarded for his resilience. When the chance came to break Del Potro in the 12th game, Murray did so at the third time of asking. A second emotional, golden triumph, four years after his last, was his - an incredible feat, unmatched by any other player, man or woman, in history.

"The fact that it hasn't been done before obviously shows that it's very hard," Murray said. "I'm very proud to have been the first one to have done that.

"It hasn't obviously been easy because a lot can happen in four years, especially for tennis players. We have so many events. Since London, I had back surgery, as well. So many things can change. My ranking dropped a lot during that period and I've gone through some tough times on the court, as well.

"I'm happy that I'm still here competing for the biggest events," he added. "I'll try and keep going. Who knows about Tokyo [2020]. But if I'm still playing in four years, when I'm 33, I don't imagine I'll be playing the same level as now. I'll try and enjoy tonight's win."

It was an emotional end for Del Potro too, but the Argentine was far from disappointed to come away from this week with silver.

"This will be for the rest of my life on my mind," he said. "I never thought something like that at the beginning of the tournament. It's even bigger, like a dream. Now I got a silver medal, which means a gold for me. I cannot believe I will bring another medal for my country."

If there were any doubts that Del Potro's creaky wrist would be able to stand up to further rigours after a week that had seen him stun two of the top three seeds in Djokovic and Rafael Nadal, they were soon buried. The Argentine's performance was remarkable, albeit breathless.

Just when you thought his rangy frame needed a lie-down, he got up and ran himself into the ground all over again.

"I cannot describe how I did tonight," Del Potro said. "For sure, the crowds make me run all the time, one more ball. I never give up because of them, because I saw my team, I saw all the Argentinian people who came to watch me in the finals. My country was behind me watching on TV. I felt all of these things on court. That's why I tried to never give up and fight until the end point."