"I was feeling many, many things before the match, more than any other match. In the finals, playing Serena. I just tried to breathe as much as I could from the moment I woke up until the match. I tried to just do that throughout the whole match, to just keep my nerves in place," Andreescu was quoted as saying by www.usopen.org.
"It wasn't easy at all, but I think that's what I've been doing really well throughout this whole year."
Williams was denied a record-equalling 24th Slam title as the 19-year-old Andreescu on Saturday became the youngest Grand Slam winner since Maria Sharapova at the 2006 US Open, when the Russian was 18.
After the Canadian bagged the first set 6-3, Williams embarked on a run of four straight games to level the set from 1-5 down to 5-5. From there, Andreescu won 7-5.
"I had some doubts because I've witnessed her come back from being 5-0 down, 5-1 down, 5-2 down. I just told myself to stick with my tactics. She started playing much better. I think the crowd really helped her, as well," the teen champion said.
The atmosphere inside the Arthur Ashe Stadium was unbelievable as the partisan crowd egged Willams on. "I was blocking out the noise, or trying to. I could barely hear myself think really. It was really, really loud. But I guess that's what makes this tournament so special...
"However, it definitely wasn't easy, especially when she started coming back in the second set. I mean, it was expected. She's a champion. That's what champions do. She's done that many, many times throughout her career," said Andreescu, the first Canadian woman to win a Slam singles.
"I just tried to stay as composed as I could. It's hard to just block everything out, but I think I did a pretty good job at that," she said.
Andreescu became the fastest player to grab a first Slam crown in the Open era after Monica Seles who lifted the 1990 Roland Garros trophy in her fourth major.