Serena Williams described her ASB Classic defeat to Madison Brengle as "obscene" and suggested she had "never returned like that in my life".

The former world number one was a shock second-round victim on Wednesday as Brengle recorded the biggest win of her career, the 26-year-old winning 6-4 6-7 (3-7) 6-4.

Mistakes littered Williams' game throughout their two hours on court, the 35-year-old particularly hampered by the windy New Zealand conditions.

Her footwork was far from smooth, but she highlighted her returning as a major weakness in her performance.

"I really think I played um, I'm trying to think of a word that's not obscene... but that's pretty much how I played," she told a media conference.

"Eighty-eight unforced errors is too much, just way too many. It's a lot. I can't expect to win hitting that many errors. I couldn't get used to the wind; my opponent was playing in the same conditions, and maybe the wind was more suited for her game, but it was really annoying me for whatever reason.

"I felt good [after the second set], but I never got in my rhythm, I didn't hit any returns in the vicinity of the court. I think I probably have never returned like that in my life so a little frustrating, especially since I worked so hard in the off-season, but at least the conditions won't be like this in Melbourne.

"She obviously did a much better job than I did. I really abhorred the conditions. I don't think I've ever hit 88 errors in my career; I could Google that and that's probably accurate. So there's no need to look back on such a crappy game!"