His victory came on a day when fellow countryman Ezekiel Kemboi, who was seeking a third gold medal but ended up being disqualified after finishing third behind Evan Jager of the United States, announced he was retiring at the age of 34.

The 21-year-old Kipruto, already a double world silver medallist and unbeaten all season, was certainly favoured here, but no-one would have bet against yet another winning flourish from the inimitable Kemboi, winner of the Athens 2004 and London 2012 Olympics, and with the last four world titles also to his credit.

As things turned out, however, Kemboi could not match the final lap surge of his younger colleague and, as he turned into the final straight he became the prey of Jager - whose name means hunter in German - who had led the field at 2,000m, eventually coming third in 8:08.47.

It looked like the veteran had another medal - but several hours after the race it emerged he had been disqualified for stepping off the track at the final water jump.

This followed an appeal by the France's European champion Mahiedine Mekhissi-Benabbad, who finished fourth and now takes the bronze.

"A protest was presented by the French team after the 3,000m steeplechase men final against Kenyan athlete Ezekiel Kemboi ... claiming he had stepped off the track," said an International Association of Athletics Federations (IAAF) statement.

 An appeal jury "met and examined the video of the race, confirming that Kemboi, after clearing a water jump, had stepped outside the track on the curved part before the home straight."

Jager, who said before the Games that he had gained valuable experience in finishing sixth at last year’s AAF World Championships, became the first US athlete to win a medal in this event since Brian Diemer took bronze in 1984, collecting silver in a time of 8:04.28.

"The Rio steeplechase was my last race after a long career of 18 years," said Kemboi, who has also been celebrated down the years for his crazy dancing in the aftermath of victory, along with his penchant for swerving out into lane seven or eight to cross the line  - he has normally had enough time to do so with impunity.

“This is my fourth Olympics and I just want to say that I am retiring from athletics,” Kemboi added.

So confident was Kipruto that he began waving to the crowd before he got to the final straight.

"I knew nobody was going to catch me, so I started celebrating, I was so happy because I knew I was going to win the gold in the last 200 metres," he said.

He revealed afterwards that Kemboi had tried to psych him out before the final.

"I did a wonderful job to beat Kemboi in the Olympics,” he said.

“I think because he was focusing so much to retire with a gold.

“But I was ready to beat him.

“I was a big competitor for him.

"He told me he was going to win.

“Kemboi usually destroys somebody's mind, but I told him, 'Let the track show who is to be the king.'"

Jager added: “Down the backstretch Kemboi took a glance back at me and in that moment I thought I might have him so I just stuck with him.

"I didn't know I had a medal wrapped up until 100 metres left to go and as soon as I got over the last barrier I could enjoy it.

“I experienced complete joy as I crossed the finish line.

“I think I had the perfect race today and I was just enjoying every second of it.

“In my eyes Kemboi is still the greatest of all time, no matter how old he is.

“I am very proud to have beaten him in a Championship-style race."

Elsewhere in the opening session of day six of the athletics programme, there was a shock exit for Poland’s double world hammer champion Pawel Fajdek, who could only reach 72.00 metres in qualifying and failed to make the top 12 places for the final.

Ashton Eaton of the US, seeking to become the first decathlete to successfully defend the Olympic title since Britain’s Daley Thompson won in 1980 and 1984, leads the overall rankings after the first three events of the 100m, where he clocked 10.46sec, the long jump, which he won with 7.94m, and the shot, where he produced his best performance in an outdoor global Championships, recording 14.73m to reach a three-round total of 2,803.

Damian Warner of Canada, who set an Olympic best time within the decathlon event of 10.30 in the 100m, is in silver position with 2,708 ahead of France’s Kevin Mayer, winner of the shot with 15.76m, who is on 2,699.

Alarm bells went off briefly for Britain’s Mo Farah as he nearly fell in his 5,000m heat after a collision with Omar Mead of the US, who hit the deck and failed to qualify.

Farah, who is seeking another 5000/10,000m double here after achieving it at London 2012, retained his title at the longer distance despite being knocked over during the race.

He stumbled but carried on to take the third automatic qualifying place.

But Kenya’s Caleb Ndiku, who took silver behind him at last year’s World Championships in Beijing, failed to progress.