Guzman was chalked off the card after turning up at the weigh-in eight pounds too heavy and his 12-round fight with Mosquera for the vacant WBA interim junior welterweight title was scrapped.
Veteran Rivera (35-17-3, 24 KOs) stepped in at late notice but with just 24 hours to prepare he was always going to struggle at the Kissimmee Civic Center.
Mosquera (33-2-1, 18 KOs) took control of the fight in the third round and never relinquished his hold. And when Rivera failed to emerge for the seventh, the Panamanian's superiority was confirmed.
Mosquera will now turn his attentions to WBC and WBA champion Danny Garcia.
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