By Martyn Herman
RIO DE JANEIRO (Reuters) - Loyalty only goes so far when national pride is at stake which is why Brazilian tennis player Bruno Soares has no problem passing on trade secrets about his usual doubles partner.
Soares, ranked eighth in the world in doubles, joined forces with Andy Murray's brother Jamie this year and together they gelled to such dynamic effect that they won the Australian Open title in January.
At the Rio Olympics, however, the Murray brothers are together playing for Britain and have been drawn against Brazilian duo Andre Sa and Thomaz Bellucci in round one of the men's doubles on Sunday.
Soares, who with partner Marcelo Melo has a strong medal chance, said his inside knowledge of Murray's strengths and weaknesses can help his compatriots spring a surprise against the second seeds.
"I've compiled a full dossier on Jamie and handed it to Andre," Soares said at the practise courts. "Not even Jamie knows what I know about him.
"For real, Andre knows him very well, but I'll help him in any way I can. It's Brazil all the way."
Veteran Sa once partnered Jamie Murray but thinks that despite the pedigree of the two Scottish brothers, home advantage can make a difference.
"The atmosphere is completely different," the 39-year-old from Belo Horizonte said.
"When we first got here, everyone, from the bus driver to the chambermaids, everyone was sending us great energy. This energy I feel now and I've felt since day one is key."
Third seed Soares and Melo, who reached the quarter-finals in London four years ago, also face brothers in round one, twins Sanchai and Sonchat Ratiwatana of Thailand.
(Reporting by Martyn Herman; Editing by Toby Davis)