The American overcame world number 12 Kevin Anderson 1-6 6-4 6-4 to reach the semi-finals of the Australian Open warm-up and in celebration flipped off a shoe before handing one of his socks to a fan.
"We were talking about it in warm-up today... a few people have their own things," Sock told reporters in Auckland.
"I think with such a unique name that I have, we figured I might start a new tradition and give a sock away if I win."
The American started poorly against the fourth-seeded South African, who blasted seven aces in a dominant opening set in which he raced through his service games and broke the 26th-ranked Sock in the fourth and sixth games.
Sock settled in the second set and improved his return as Anderson lost range and accuracy, tying up the quarter-final on his second break and set point opportunity in the 10th game.
Anderson served better in the decider but Sock eked out another break, again in the 10th game, to seal the contest in 98 minutes.
"I thought he came out firing and did not miss many first serves, which against a guy like that, it was crucial for me he misses a few," Sock added.
"I was able to get some balls in near the end and scrap out some points. I'm looking forward to playing in the semis."
Sock will next face four-times champion David Ferrer after the Spaniard completed a 6-3 6-4 win over the Czech Republic's Lukas Rosol.
The 33-year-old Ferrer, who was granted a wild card and took the top seeding, was at his retrieving best on Thursday, forcing Rosol to continually play an extra shot, while he converted three of his four break point opportunities.
"I have to play well to beat him," Ferrer said.
"I tried to serve good and be aggressive with my forehand. The important thing is I am in the semi-finals playing good tennis."
Twice champion John Isner of the United States will not be in the last four after losing the third quarter-final 7-5 2-6 6-3 to Roberto Bautista Agut, despite firing down 17 aces.
The Spaniard will meet French second seed Jo-Wilfred Tsonga, who saw off Italy's Fabio Fognini 7-5 7-6(4) in the final match of the day.
(Reporting by Greg Stutchbury in Wellington; Editing by John O'Brien)
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