By Guillermo Parra-Bernal

SAO PAULO, Aug 7 (Reuters) - Expense controls were the defining element for the second-quarter earnings of Brazilian financial market infrastructure companies, with exchange operator BM&FBovespa SA unexpectedly delivering the best set of results during a tough market.

Fewer working days and weak trading volumes in the second quarter hampered revenue at BM&FBovespa, but earnings were helped by efforts to curb sales, general and administrative expenses and boost financial income in the quarter. BM&FBovespa is Brazil's sole listed bourse.

In the case of Cetip SA Mercados Organizados, the country's largest securities clearinghouse, net income missed analyst estimates in the quarter after a jump in payroll and capital spending eroded slim gains in securities registration revenue. Both companies released earnings late on Thursday.

Almost four years of weak economic expansion and rising government meddling in the economy have stifled investor confidence in Brazil, cutting equity market inflows and triggering price volatility. Optimism that the October presidential election will bring about a more business-friendly policy has been bolstering market activity in recent weeks.

São Paulo-based BM&FBovespa earned 250.1 million reais ($109 million) in the quarter, compared with an average 249 million reais in a Reuters poll of seven analysts. While revenue plunged 22.5 percent on an annual basis, expenses rose a meager 0.8 percent, and financial income jumped 38 percent in the period, according to a securities filing.

"We remain confident that adjusted expenses will grow below annualized inflation throughout this year," Chief Financial Officer Eduardo Guardia said in the filing. To partially mitigate the impact of the weak business outlook on shares of the company, BM&FBovespa will stick to an 80 percent dividend payout ratio and a share buyback program that already has repurchased the equivalent of 3.5 percent of shares outstanding.

Equities and derivatives volumes sank 18.7 percent and 37.9 percent on a sequential basis, respectively. Expenses, though, missed the poll's estimate of a 4.2 percent decline.

In the case of Cetip, the resilience of its business model and new products helped bolster earnings despite a surge in expenses. Clearing and custody activities performed in line with expectations, while registration receipts suffered amid poor listing of financial securities.

The liens unit had small volume growth but has slowly begun to recover.

The company posted net income of 99.5 million reais, below the poll's estimate of 106 million reais for the quarter. On an annual basis, net revenue rose 6.4 percent, slightly above the poll's forecast of 6.2 percent, while general expenses jumped 11.1 percent after capital spending spiked. The poll expected a decline of 8.2 percent in expenditures.