MEXICO CITY/SAO PAULO (Reuters) - Billionaire Carlos Slim's Grupo Financiero Inbursa SAB (>> Grupo Financiero Inbursa SAB de CV) on Friday took a key step to expand outside Mexico after agreeing to pay $45 million for the Brazilian unit of South Africa's Standard Bank Group (>> Standard Bank Group Ltd).

The purchase of Banco Standard de Investimento Ltda gives Inbursa a services platform akin to the one it has at home, the lender said in a securities filing. The move comes as rival Brazilian banks such as Grupo BTG Pactual SA (>> Grupo BTG Pactual) and Itaú Unibanco Holding SA (>> Itau Unibanco Holding SA) opened broker-dealer units in Mexico, the region's No. 2 economy after Brazil.

The Inbursa-Standard deal underpins an overseas expansion push among Latin American banks, which have gained expertise and beefed up capital in the wake of years of robust growth. Part of that expansion, analysts said, will be made possible as global banks pull back amid an economic recovery in the United States and other developed economies.

Inbursa is Mexico's sixth-largest bank with 482 billion pesos ($36.4 billion) in assets, equivalent to 7 percent of the country's banking assets. In contrast, Banco Standard cut assets by over 90 percent to 244 million reais ($102 million) over the past year, with its capital base down by more than 60 percent.

The sale of Banco Standard, which came to Brazil in 1998 and at some point worked in bond underwriting, financial advisory and cross-border deals between Brazilian and African companies, is part of a wider strategy by Johannesburg-based Standard in order to focus on Africa. Standard, Africa's largest lender by assets, has in recent years exited Argentina and sold assets in Turkey.

Shares in Inbursa fell 0.9 percent to 29.10 pesos on Friday. Shares in Standard Bank, which is 20 percent owned by Industrial and Commercial Bank of China Corp (>> Industrial and Commercial Bank of China) closed up 1.1 percent at 124.29 South African rand.

(Reporting by Elinor Comlay, editing by G Crosse and Lisa Shumaker)

By Elinor Comlay and Guillermo Parra-Bernal