LONDON — Anthony Joshua stopped Charles Martin inside two rounds to snatch the IBF heavyweight belt off the American in only his 16th professional fight on Saturday.

With two knockdowns in the second round at the O2 Arena, Joshua secured a crushing knockout victory that means Britain's Olympic champion holds the leading amateur and professional heavyweight titles.

The 29-year-old Martin (23-1-1) won the vacated belt in January, and this was his first defense, and the first loss of his pro career.

The 26-year-old Joshua is the first boxer to win the world heavyweight title while being the reigning champion in Olympic boxing's top weight division of super-heavyweight. Muhammad Ali was the Olympic light-heavyweight champion when he beat Sonny Liston in 1964 to become world heavyweight champion, in his 20th fight.

Almost four years after Joshua claimed gold for Britain at the London Olympics, the venue was different in the capital but there was the same raucous home support to see another dominant victory by the humble fighter.

Martin had made a brash arrival in the ring, sporting a bejeweled crown but his bravado was not matched by his performance against the younger, more clinical contender.

After being dropped by Joshua in the second round, Martin got back up but was immediately grounded by another Joshua right. This time, Martin didn't beat the count.

All 16 of Joshua's wins since his pro debut in 2013 have been by KO.

"I come to knock people out," Joshua said. "It's about speed and precision."

Joshua also said he would punish IBO/WBA/WBO champion Tyson Fury for his trash talk.

"The promoters are going to do their promoting, the fighters are going to do their fighting and the public are going to do their talking and I'm going to keep on walking," Joshua told the BBC.

"I'm going to walk through Tyson Fury when's he's ready. I'm not messing around believe you me. Scrap all this 16 fight nonsense. I'm training hard and I mean business. I'm here to stay and I want to make some real noise in this division.

"That belt. I got big respect but I want to do more. If I get too carried away I feel that I'll get complacent. So let's put that bad boy away.

"Let's put that with the Olympic medal and let's go on and get more and keep entertaining these boxing fans.

"That's what I'm here to do. I'm young, I'm fresh and honestly I'm looking forward to getting back in the gym.

"I have got skill. I'm not just some beach body boxer. I train hard and this is just the results. IBF champion and I'm very, very happy. I'm happy for the UK as well."