BRENTWOOD, U.K. – Britons’ love affair with Ford’s newly imported Mustang deepened this week when one was piloted over a 430-mile (692-km) open public road course to win a best improved-fuel-economy title.

Entered as Ford’s contestant in this year’s MPG Marathon, the 5.0L V-8 Mustang Fastback achieved an average 30.5 mpg (7.7 L/100 km) compared with its official homologated economy figure of 17.4 mpg (13.5 L/100 km), a 58.2% improvement.

The result dwarfs the previous highest-economy marathon improvement of 39% set in 2014 by Formula Ford drivers at the wheel of a Fiesta ST.

The Mustang already has won the hearts and wallets of U.K. motorists by topping both the sports car sales charts and the residual-value tables, fending off premium challengers including Porsche, BMW and Jaguar.

“The Mustang was perfect for the MPG Marathon owing to brilliant steering, handling and road-holding,” Ex-Works rally team Andy Dawson and Andrew Marriott say in a statement. “We were able to let the ’Stang follow the road, with minimal brake use or wasted energy.”

The pair has a stellar MPG Marathon track record, having set the benchmark at 90.6 mpg (2.6 L/100 km) in a Ford Fiesta 1.6 TDCi in 2012.

“Since right-hand-drive Mustang arrived here at the beginning of the year, over 3,000 have been delivered to proud new owners – two thirds of them with 5.0L V-8 engines,” says Kevin Griffin, sales director-Ford of Britain. “They powered Mustang to the top of the sales charts as the U.K.’s top-selling high-performance sales car.

“But a high power rating need not necessarily mean excessive fuel consumption – as this year’s MPG Marathon has demonstrated.”

The Best Outright MPG title was claimed by a Mazda 2 1.6L Sport with overall consumption of 76 mpg (3.1 L/100 km), an improvement of 6.9%.