Charlie Edwards retained his WBC world flyweight title in dramatic circumstances at the O 2 Arena after initially being stopped – only for video evidence to overturn the verdict.

The popular Londoner took a knee in the third round after his hard-hitting Mexican opponent Julio César Martínez had rattled over 20 unanswered punches to his head and body. But with Edwards on the floor, Martínez then fired in an illegal shot to his ribs, which left him crippled in pain.

That punch was missed by British referee Mark Lyson, officiating in his first world championship fight, who immediately stopped the fight.

Minutes later, it was announced that Martínez was the new champion, to loud booing. However, WBC supervisor Mauricio Sulaiman was watching the video replays from ringside and ordered the fight to be declared a no contest. “I truly believe in instant replay,” explained Sulaiman. “The kid was hit while he was down. It was an accident. There’ll be an immediate rematch.”

Edwards, who admitted that he had struggled to make the flyweight limit after being interviewed when he thought he had lost, was delighted at the reversal.

“This is the right decision,” said Edwards. “I took a knee for a purpose. He finished me off with a body shot and I could not recover. Cheaters never prosper. We get in this ring to abide by the rules.”

The promoter Eddie Hearn, who called it “one of the most bizarre things I have ever seen”, was in no doubt it was the right decision. “The shot was not late, it was next week. It was a blatant low blow.”

Earlier on the card the hard-hitting Joshua Buatsi extended his unbeaten record to 12-0 with a seventh-round knockout over Ryan Ford.

Ford, a teak-tough fighter from Canada who has previously done time for armed robbery, was chosen to give Buatsi some rounds and he obliged until the south Londoner stepped up the pace in the second half of the 10-rounder. However, there was another controversial finish as Ford screamed “low blow’’ after being sent to the canvas with a right hook to the body followed by a hard left. “I never make excuses but he hit me with a low blow,” said the Canadian, who drops to 16-5. “But it is what it is. I respect him and hopefully one day he’ll come to Canada and we’ll give it another go.”

Buatsi, who won bronze at the Rio 2016 Olympics and increasingly looks the real deal in the pro ranks, gave credit to his opponent. “He pushed me hard. He’s a tough fighter. He also hit me on the back of the head. It’s a tough sport. But all credit to Ryan.”

Wales’s Joe Cordina looks another former Olympian going places and he further enhanced his reputation by defeating Gavin Gwynne in the battle of the unbeaten fighters to retain his British and Commonwealth lightweight title.

Both men had their moments but Cordina, who was a part of Team GB’s 2016 Olympic squad, produced by far the crisper work and he was also impressively calm whenever Gwynne put him under pressure as he secured a widespread points verdict.

Both men were docked points, Cordina for a low blow in the seventh and Gwynne for repeatedly hitting his man on the back of the head in the ninth, before Cordina was given the verdict by 116-110 on two cards and 116-111 on the other, which felt about right.

“As the fight went I started catching him but he definitely has a hard head,” said Cordina, who moves to 10-0. “He was extremely fit and tough guy.”

Earlier in the night, Savannah Marshall, who was Britain’s first woman’s world champion as an amateur, continued her unbeaten record to 7-0 with a fifth-round stoppage of the Brazilian Danielle Basteri.

The 28-year-old Marshall, who carries the nickname the Silent Assassin because of her shyness, blooded her opponent’s nose in the second and continued to dominate before putting Basteri down in the fifth, after which referee stopped the fight.

Marshall believes her professional career has not progressed as rapidly as she expected but says a showdown with the American Claressa Shields, who she beat as an amateur, is now inevitable.

“Claressa is the undisputed middleweight champion so in that respect she is ahead of me,” she said. “I believe that the fight will happen soon and that I will beat her again, like I did as an amateur.”