Up against John-Patrick Smith at Melbourne Park, Thompson emerged a 6-1 6-3 1-6 6-7 (2/7) 9-7 victor to win the week-long play-off series between Australian players for the second year in a row.
The 20-year-old described the match, played in temperatures in the mid-30s Celsius, as “the most gruelling” of his career to date.
In the final set – forced by Smith after he had fought back from two sets down – both men were suffering from cramp. In it, Smith led 3-0 and had two points at 15-40 for a double break. However, Thompson dug in, then broke back before pushing on to win the contest, serving it out at the third time of asking.
“It means the world (to win), to play another home Grand Slam is amazing,” said the world number 274 after his memorable success.
In the women’s final, Russia-born Daria Gavrilova beat Arina Rodionova 6-4 6-2 to book her place in the Melbourne main draw.
Rodionova led 3-1 early on but from that point lost 11 of 14 games.
Gavrilova, 234th on the WTA rankings, qualified for the Australian Open in 2013 and reached the second round of the main draw but missed this year???s tournament after undergoing knee surgery.
The Australian Open gets under way on January 19.
Kai-Chen Chang and Ze Zheng had already won wild cards via the Asian play-off, while Denis Kudla and Irina Falconi earned the main-draw spots reserved for US players with their recent performances on the USTA’s Pro Circuit.