[5] Lord Derby sent the filly to his private trainer Walter Earl at his Stanley House stable in Newmarket, Suffolk.
[7] In autumn, Sun Stream ran in the six furlong Cheveley Park Stakes, Britain's most prestigious race for two-year-old fillies.
[8] Sun Stream began her three-year-old season in the seven furlong Upwell Stakes, a now discontinued race which served as a trial for the 1000 Guineas, in which she finished second to Exotic.
[6] Two weeks later, on VE Day, Sun Stream started 5/2 favourite for the 1000 Guineas which, because of the war, was moved from its traditional venue on the Rowley Mile to the adjoining July course.
Sun Stream's success gave Lord Derby a seventh win in the race as both owner and breeder,[1] and was very popular with the unusually large crowd.
The relaxation of wartime restrictions on transport resulted in a huge crowd converging on Newmarket, leading to serious traffic congestion at the course.
In what was described as "one of the most exciting classic finishes ever contested",[10] Sun Stream won the race by a short head and three quarters of a length from the Aga Khan's Naishapur and Solar Princess.