The 21-year-old welterweight was beaten on points by Francisco Armento in Group B of the World Series of Boxing competition.
Pattinson was fighting for the British Lionhearts, who lost 4-1 to the Mexico Guerreros.
The Birtley Amateur Boxing Club fighter lost 2-1. Judges Roberto Servide, from Argentina, and Enrico Licini, from Italy, scored the bout 49:46 to Armento but US judge Thomas Cleary went in Pattinson's favour, 47:48.
In an Instagram post, Pattinson said: "Lost in a close fight which I thought I won on better work. Was always going to be a tough job."
He is now looking ahead to an Olympic qualifier.
GB Boxing has named him in a 13-strong squad for the European Olympic qualification event, running from next Thursday to Monday, April 18, in Samsun, Turkey.
It is the first of four Olympic qualification events this year, and there will be 36 places for Rio 2016 on offer. Three places are available at each of the 10 men’s weights, and two slots are on offer in each of three women’s weight categories. Pattinson has been selected for the 69kg class.