Caroline Wozniacki said players are virtually powerless to stop Serena Williams when the world number one is on song.
The American, 32, claimed her 18th major title on Sunday, triumphing at the US Open in emphatic fashion - rounding out a dominant fortnight with a 6-3 6-3 win over Danish 10th seed Wozniacki.
Williams was not pushed beyond 6-3 in any set she played at Flushing Meadows, in one of the most one-sided grand slam tournaments.
It was the fifth time Williams went through the two weeks of a major without dropping a set.
Wozniacki said Williams' record, which sees her tied for fourth on the all-time list of singles majors winners, spoke for itself.
"I think her results and her career says it all: 18 Grand Slam titles. You don't get that unless you're exceptional in what you do.
"She is one of the greatest of all time. To have 18 Grand Slam titles and still be the person she is is really something very rare.
"I admire her both on and off the court. I definitely think when Serena is on her game there's not much we can do. So I think that's why she has so many titles that she has."
As easy as Williams makes it seem, it is not all smiles and trophies, according to Wozniacki.
"I don't believe that talent can beat everything. She's a hard worker. She works hard every day, just like us, but when she needs to she can pull out that big serve. She has the power," the two-time US Open finalist said.
"She can push us back on the court and take the initiative.
"She definitely has the experience now, as well. I think that makes it even harder, because maybe back in the day she might have made not the right choices.
"Now she knows what she needs to do out there, and it makes it even harder to beat her."
Wozniacki, who was last in the final in New York in 2009, said she was overwhelmed in her second major decider.
"I was a little nervous going out there.
"When you walk into the stadium and people are screaming so loud you can't hear what you're thinking yourself, so it's kind of overwhelming.
"But it's such a cool experience. I just wanted to get a good start. I knew that against Serena, you have to have a good start, otherwise she starts going in and being even more aggressive. You're kind of done.
"So I didn't get the start I wanted. Then all of a sudden see myself going behind and it's tough to get back."