Depending on how you count 'em, Ford (F 0.57%) owns the top-selling car in the Focus, globally selling 589,709 of them through June, up 20% from last year. That beats out Toyota's (TM -0.01%) Corolla, and if the pace holds through for the rest of the year it would mark the second year in a row that Ford can lay claim to the best-selling car in the world.

Toyota, though, isn't throwing in the towel yet and contends that if you count the Matrix, which is essentially a Corolla hatchback, along with all the other "Corollas" it sells under different nameplates, it's the winner.

Ford's claim is based on global vehicle registration data provided by the auto research firm Polk, which confirms that Ford's numbers are accurate, but can't comment on Toyota's numbers unless that carmaker releases them. Toyota is said to be preparing a response.

Last year Ford sold 1.02 million vehicles as sales jumped 40% from 2011, and the contest with Toyota might not be so close this year if U.S. sales weren't so weak. So far this year, the Focus is up only 1% to 188,654 vehicles through September, though overall the carmaker's sales are 8% higher over that same period from a year ago. The lackluster performance is forcing Ford to idle the Michigan assembly plant for two weeks during the fourth quarter where the Focus and the slow-selling C-Max hybrid are made.

China is Ford's best market for the Focus, accounting for a third of global Focus sales; it also pushing sales higher for Ford's entire lineup of cars. Sales in China soared 137% over the first six months of 2013, putting Ford in line to sell more than 6 million cars globally this year.

It's not just Ford seeing a big uptake in Chinese sales this year: General Motors (GM 5.44%) is seeing big gains too. Earlier this month it reported that September sales jumped 13.7% in the country following an 11.2% gain in August, which itself followed a record month in July.

China has already become one of the most important markets in the world for carmakers, with 15.9 million vehicles sold there already through the first nine months, which is slightly more than what's expected to be sold here at home for the entire year. China saw a 21% jump in car and light truck sales in September, rising to to 1.59 million units, the highest number achieved since January, and it's on track to sell over 20 million cars in 2013.

Ford sales in China jumped 61% to 96,111 units last month, driven in large part by the popularity of the Focus, which was the country's top-selling car in September (though it lags VW's Lavida year to date). Ford has launched six new vehicles in China this year and is working hard to make up for having come to the market late in the game.

So, in this race to the top, is the Focus No. 1 as Ford claims, or does Toyota have a point that you have to take into account all the nameplates? Let us know in the comments below.