Mieres scored his best result of 1953, however, in the non-championship Grand Prix de l'Albigeois held in Albi, France, finishing in fourth place. He also finished third in a sports car handicap race at Caen in July 1953, which was won by Jean Chancel. In January 1954 Mieres came in second at the Buenos Aires Grand Prix. Maurice Trintignant was victorious after Mike Hawthorn skidded close to the finish. The tail of Mieres' Maserati caught fire during the 1954 Belgian Grand Prix at Spa Francorchamps. After belatedly realising this, he slammed on the brakes and jumped to safety. Mieres then finished fifth in a Maserati at the 1954 British Grand Prix at Silverstone. In the 1957 City of Buenos Aires sports car race Mieres drove a 3.5 litre Jaguar to a fourth-place finish. His driving partner was Ninian Sanderson of Scotland. Mieres later teamed with Anton Van Dorey for a win in the 1959 USAC Road Racing Championship Daytona 1,000 km, the predecessor to the modern Rolex 24 at Daytona.