Boxingtalk has been informed that WBO welterweight champion Antonio Margarito will make the mandatory defense of his title against undefeated challenger Paul Williams on HBO on July 28. The replay of the July 21 Hopkins-Wright PPV will open the telecast. Margarito-Williams will close out an unusually busy July for HBO. The first three Saturday's are as follows;  On July 7, as first reported by Boxingtalk, IBF heavyweight champion Wladimir Klitschko will look to avenge his loss to Lamon Brewster. On July 14 Arturo Gatti returns against a 'contender' and on July 21  Hopkins and Wright battle for light heavyweight supremacy on HBO PPV.  (10:30 AM EST)