In 1948 Tregonning played in the Australian Championships, losing to Jack Crawford in a four set Round 2 match. The same year he partnered Mervyn Rose in the Australian Championships doubles competition again reaching Round 2. In 1949 Tregonning lost a Round 2 Australian Championships match against Bill Sidwell, but partnering Rose was able to secure a spot in the quarter-finals of the doubles competition. In the 1950 Australian Championships Tregonning once again reached the second round, however, losing a first round doubles match in which he partnered Philip Brophy. Tregonning received direct entry into the
Men's Singles draw of the
1951 Wimbledon Championships but lost in the first round to Brazilian
Armando Vieira. Tregonning partnered
Peter Cawthorn in the
Men's Doubles and reached the third round, including a first round win against Vieira and his partner
Leon Norgarb. Partnering Rosemary Bulleid he reached the third round in the Mixed Doubles. Tregonning returned to Wimbledon in 1952, but was defeated in the first round of the
Men's Singles by
Douglas Scharenguivel. He again partnered Cawthorn in the
doubles event, but they were defeated in the first round by Americans
Irvin Dorfman and
Grant Golden. He was, once again, more successful in the Mixed Doubles reaching the third round together with Gem Hoahing. In 1953 Tregonning played at the Wembley Professional Championships, then the most prominent professional tennis tournament. He was able to secure a place in the quarter-finals being defeated by fellow Australian tennis legend Frank Sedgman. Tregonning was the runner-up at the 1954 English Professional Championships and 1955 Great Britain Professional Championships.
Australian Championships match without an umpire Tregonning played in a famous 1953 Australian Championships Rd1 match in which the umpire left the grounds to "go to (his) tea," leaving the two players – Tregonning and fellow Australian
Brian Tobin – without an umpire or any ball boys. Harold Cornish, the President of the Victorian Umpires Association, took over, although by this time most of the spectators had left with only eight spectators and three representatives of the press remaining. == Coaching career ==