(CNN) With his index finger pointing to his temple, it was a gesture that came to define the 2016 US Open.
Once considered too mentally fragile to win on the biggest stage, Stan Wawrinka believes his psychological toughness helped him clinch his first US Open title and third grand slam crown at an engrossed Flushing Meadows on Sunday.
So long in the shadow of his fellow Swiss and 17-time grand slam winner Roger Federer, Wawrinka made the gesture several times during his 6-7 (1-7), 6-4, 7-5, 6-3 victory over defending champion Novak Djokovic.
"It started in the Australian Open when I beat Novak (in the quarters) for the first time," Wawrinka said about the gesture during an interview with CNN's James Blake at Arthur Ashe Stadium in New York.
"It just came like that. I never try to think what I am going to do. You can see after the match, when I don't do anything, because I am completely empty and dead and all the emotions coming."
It was in January 2014 that Wawrinka beat Djokovic to reach the Australian Open semifinals.
"This for me is really when I started to be tough with myself," said Wawrinka, who also overpowered Djokovic in the finals of Roland Garros last year. "I know if I want to have a chance to beat the top players, I need to be mentally ready for that."
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The third-seeded Swiss showed his mental strength several times across the last fortnight.
Down match point in the fourth-set tie-break against Briton Dan Evans in the third round, Wawrinka slammed down a big serve and won the point with a crisp volley. He ended up winning in five sets.
"I won that match and little by little, I started to play better each match," Wawrinka said.
"Saving match point, you have be a little bit lucky," said the Swiss after adding the US Open to his 2014 Australian Open and 2015 French Open titles.
"But I was happy with what I was doing, I was fighting, staying positive, trying to find a way."
After getting past Evans at Flushing Meadows, Wawrinka beat 2009 winner Juan Martin Del Potro in the quarterfinals and 2014 finalist Kei Nishikori in the semifinals as the heat and humidity soared in New York in the tournament's second week.
"This was the most difficult slam I ever played," Wawrinka said. "Physically, mentally, we had some tough conditions in the last few days."
"And right now I am really tired, I am completely empty. After the match win, it was almost too much, I was really tired. But I am really happy."