In its list, Opower took the actual matches of Brazil versus Mexico, Japan against Colombia and Germany versus the United States, declaring the winner based on how well each conserved power and reformed its energy sector. Under those criteria, the study's result foreshadowed the Brazil-Mexico match that ended in a tie.
Both countries "are taking significant measures to become energy efficient, but are facing big challenges," Fischer told CNBC. "They have a growing middle class that's using more electricity and has infrastructure limitations."
Opower points out that Brazil's rapid growth has been accompanied by a big jump in middle-class citizens who consume more energy. Latin America's largest economy generates nearly 80 percent of its power via eco-friendly hydroelectric dams, yet those efforts have been complicated by a surge in demand for electricity, as well as a dry spell that has depleted reservoirs.
Read MoreBrazil's own goals
Conversely, Mexico has a profile similar to Brazil's: rapid growth and a large group of the upwardly mobile middle class that is drinking up power. Broad efforts to reform its energy sector are laudable, Opower writes, "but what it means for energy efficiency at this point is not entirely clear."
When Japan squares off against Colombia next Tuesday, Opower believes it's the world's third-largest economy that will have the edge based on energy efficiency.
After the 2011 disaster at Fukushima, the country has replaced nearly half its nuclear power through energy conservation, the firm notes. According to International Energy Agency data, Japanese households use less than half of the power eaten up by the U.S.—the world's largest energy consumer.