Although Iso's Bizzarrini-built A3/C should have theoretically raced directly against its most obvious rivals, homologation requirements forced it into contesting the prototype categories. As a result, A3/C's were often up against cars like Ferrari's 275 and 330 P's, Corvette Grand Sport's and Ford GT40's - machines that had been designed with practically no concessions for road use. However, with organisers varying class types from race to race, A3/C's were also able to compete in less hotly contested over five-litre categories from time to time. This would have suited Iso just fine as the firm would be able to pick up the odd class victory while at the same time arguing their A3/C was being forced to run against more highly developed machinery. The car made its international debut during March 1964 with Ed Hugus, Sonny Wilson and Bill McLaughlin entering Sebring's 12 Hour race. Chassis B 0202 had only just been delivered to McLaughlin and although being plagued with a troublesome gearbox on the day, this car would go on to win a regional SCCA title in 1964.

Bizzarrini's original Turin prototype, B 0201, was the next A3/C to race, Frenchmen’ Pierre Noblet and Fernand Tavano taking the wheel for April's Le Mans Trials where Noblet posted the fastest qualifying lap of the two. Late in May, B 0201 was taken to Germany for the ADAC Nurburgring 1000km race with Noblet joined by Swiss Bizzarrini stalwart, Edgar Berney, the pair going on to finish 19th overall and an impressive second in the over five-litre prototype class. Then as now, endurance racings showpiece Le Mans 24 Hours was the most important outing of the year. Bizzarrini prepared a new Corsa, chassis B 0207, as the sole Iso entry for this gruelling event where it ran under the banner of French Iso and Bizzarrini Concessionaire, Auguste Veuillet’s Societe Sonauto. Against all expectation, Noblet and Berney completed the French classic in 14th position overall, good enough for a fantastic first in class. From Le Mans, B 0207 was then taken to Rheims in July for the same drivers to participate in the 12 Hour race. But despite having run well within the top ten, they retired at half distance.

Two Swiss hillclimbs were on Bizzarrini's agenda for late August and victory in the over five-litre class (fourth overall) at St. Ursanne was followed by a tenth overall and second in class at Sierra Montana. The firm then entered two A3/C’s for the Paris 1000kms during October, Noblet and Berney in 0201 and Italian's Mario Casoni and Odoardo Govoni in B 0207. Casoni and Govoni were immediately on the pace at Montlhery and finished eleventh overall and third in the over five-litre category, just behind the first and second placed Ferrari prototypes of Maranello Concessionaires. Noblet and Berney came in a respectable 21st overall for fifth in class. The final outings for 1964 came towards the end of October, Bizzarrini entering two cars for the Ettore Betoja 3 Hour Trophy at Monza. B 0207 was under the guidance of Casoni who went on to finish second while Antonio Finiguerra finished seventh in B 0201. Thus, the A3/C gave a creditable account of itself during 1964 and despite having often been forced to run against prototypes from major manufacturers, had recorded that all-important Le Mans win.