In the following season she was one of the best horses in Britain, scoring classic victories in the 1000 Guineas and St Leger Stakes as well as winning four other races including the Jockey Club Cup and Newmarket Oaks.

[4] In the Gimcrack Stakes at York Racecourse Tranquil finished second, beaten four lengths by Town Guard, who was regarded as the season's best juvenile colt.

[12] The ground at Newmarket was unusually hard and dry in the late summer of 1923, and Lord Derby decided to send the filly temporarily to the stable of Jack Joels trainer Charles Morton at Wantage.

[14] On 13 September at Doncaster Racecourse Tranquil was ridden by Tommy Weston in the 148th running of the St Leger over fourteen and a half furlongs and started at odds of 11/1 in a thirteen-runner field.

[12] On her next appearance Tranquil ran in the Jockey Club Stakes over fourteen furlongs at Newmarket on 4 October for which she started the 1/3 favourite and finished third behind the colts Inkerman and Legality.

[15] On 1 November at Newmarket Tranquil was moved up in distance for two and quarter mile Jockey Club and won by a length and a half at odds of 1/5[16] from Abe Bailey's colt Apron.

[17] Tranquil won two other races in 1923, namely the Newmarket Oaks over 14 furlongs and the Liverpool St Leger on 7 November, beating the colt Twelve Pointer by a head in the latter event.