In making it to the quarters at Melbourne Park the American progressed past the fourth round of a grand slam for the first time since the 2010 US Open, with injuries and illness having stymied her in recent years.
As such, her performance at the year's first major was better than many would have expected, but while satisfied to have taken steps in the right direction, Williams was not happy with how she played in her loss to Keys.
“I think a lot of players would have been happy with this tournament. I'm happy with progress. I'm not happy with a loss, I'll tell you that,” she said.
“I just don’t think I played as strong of a match as I would have liked. I think it was pretty rare that I was able to string together three or four points without an error. That was unfortunate for me.
“Getting into a quarterfinals, you really want to come out and play your best. Even if you don't, you want to play yourself into the match, take your opportunities. I’ll learn a lot from this loss.”
The seven-time Grand Slam singles winner admitted that she struggled to retain her momentum after Keys took an injury time out in the second set of the encounter.
"I felt like I really got off rhythm after that break. It was hard to come back," explained the 34-year-old.
"Never really felt like I got back to that rhythm that I was building at 4-1 and really just started to feel good about everything.
"I think for her, when you're injured, you feel a little tentative at the beginning. After a while you feel okay and so then you start to be more relaxed."
However, despite those frustrations, Williams knows that a strong showing in Melbourne on the back of winning the Auckland Open title marks a fantastic start to the year.
"It's definitely been a great last four weeks, I think," Williams said.
"A lot of match wins, a lot of momentum, just a lot of great things happening that everybody wants to happen in their career."