Ethiopia's Selemon Barega sprinted the last lap to beat world record holder Joshua Cheptegei of Uganda and win a shock Olympic gold medal in the men's 10,000 metres on Friday.

The 21-year old Barega powered down the home straight to cross the line in 27 minutes 43.22 seconds, ahead of world champion Cheptegei in 27:43.63.

Jacob Kiplimo, the youngest ever Ugandan Olympian when he ran the 5,000 heats in Rio as a 15-year old, posted a time of 27:43.88 to secure bronze in the first athletics medal event of the Games.

Barega, the 2019 5,000m world championship silver medallist who set the second fastest 10,000 metres time of the year in June, was applauded by the Ethiopian delegation as he smiled broadly on a victory lap with his country's flag draped around his shoulders.

Cheptegei said he was experiencing mixed emotions.

"I have two feelings. "One is that I'm very happy to have won an Olympic silver medal today," he told reporters. "But the other side of me is really not satisfied with the result because I came here expecting to win a gold."

Cheptegei also admitted that 2021 had been tough for him.

"This year was really a very difficult year for me in terms of racing," he said. "It's the year that I have lost all the focus, all the belief. There was a lot of pressure and I was feeling it in every moment."

Uganda's Stephen Kissa acted as the early pacemaker before dropping out a little over halfway through the race.

"We had a plan for me to go ahead to make it a fast race," Kissa told reporters. "I thought they were going to follow me but when I looked round they were not there."

Cheptegei led briefly before dropping back into the pack and Barega seized his chance, moving among the leaders in the last third of the race before hitting the front with a surge on the last lap to secure his surprise victory.