The former World No. 1, who has been a non-factor for most of the past two years. is part of the women's quarterfinals after rolling to a 6-3, 6-4 victory over eighth-seeded American Madison Keys on Sunday in New York.
The 78-minute victory at Arthur Ashe Stadium even seemed surreal to Wozniacki. Probably because the Denmark native hadn't won a single match at a major this season prior to the U.S. Open.
"This is crazy," Wozniacki said from courtside. "After such a tough year, to be in the quarterfinals here, it's amazing.
"I know I faced an American, but thank you for cheering me on anyway."
Wozniacki, who will face Latvia's Anastasija Sevestova in the quarterfinals, dominated Keys from the outset. She made just seven unforced errors while Keys was plagued by 33.
Wozniacki's four victories at the U.S. Open represent the first time she has won four in a row at a single event since early 2015. She had lost seven of her last 12 matches entering the tourney and now is one victory away from an unlikely semifinal appearance.
"I can't believe I'm here in the quarterfinals," Wozniacki said. "I was pretty nervous in the last game, telling myself, 'Please, serve, hold on for me' ... and I did. I knew she wasn't going to give up. I tried to keep it on the backhand side because that's where I felt more comfortable."
Sevestova defeated 13th-seeded Johanna Konta 6-4, 7-5 to become the first Latvian woman in 22 years to reach the quarterfinals of a Grand Slam event.
The 26-year-old is making her own comeback after retiring in 2013 due to injuries. But she returned to competitive tennis two years later and outlasted the Great Britain native in straight sets.
Sevastova broke the service of Konta -- an Australian Open semifinalist -- seven times during the match.
Italy's Roberta Vinci also claimed a spot in the quarterfinals with a 7-6 (5), 6-2 victory over Ukraine's Lesya Tsurenko.
The seventh-seeded Vinci lost to Serena Williams in the finals of last year's U.S. Open and is making another charge this year. This is her fourth time reaching the quarterfinals at the U.S. Open. She has never reached the quarters at any of the other three majors.
"I love to play here, I love this crowd," Vinci said. "I always play so good here -- maybe it's the crowd, the atmosphere, the food ... everything. Today was a tough match and I was tight in the end and right now I'm in the quarterfinals and last year the final, so what do I have to say?"