Campbell looked to be heading for a wide points win against the stubborn operator, but gradually wore Szot down and took him out with a round to spare.
Kal Yafai is the new IBF Inter-Continental super-flyweight champion after a dominant display over Nicaraguan Herald Molina.
The former amateur star was in total control from off, battering his opponent with some hurtful shots and the writing was on the wall for Molina after only round one.
A sweet left hand did the damage in the second round and the out-of-depth Molina failed to recover as Yafai, 25, recorded a ninth career stoppage since turning pro and a twelfth win in total.
Younger brother Gamal improved to 4-0 in the very next fight on the Christopher Rebrasse v George Groves undercard with a one-sided pasting of Frenchman Sofiane Bellahcene.
The 23 year-old won every round of the bout, even after suffering an injury to his right hand midway through the clash, and was rightly given the fight 60-54 on points.
Also on the bill, Swedish prospect Oscar Ahlin made it to 10-0 with a sixth round TKO victory over Olegs Fedotovs, whilst Brits Martin J Ward and Luke Watkins both scored final session triumphs.
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