Simona Halep ranked her Australian Open showing as "close to 10" after feeling like she had "hit by a train" in the first set of a fourth-round defeat to Serena Williams.

Top seed Halep had lost eight of her previous nine meetings with the 23-time grand slam champion and looked set for a hammering when she was a break down in the second set after being blown away in the first.

The world number one showed her fighting spirit to come roaring back in an enthralling contest on Rod Laver Arena, but Williams showed her fighting spirit to win 6-1 4-6 6-4 on Monday.

Halep was upbeat despite a defeat at Melbourne Park which could cost the Romanian her top-ranked status. 

A smiling Halep said in her media conference: "I will start with a joke. I felt like I had been hit by a train in the first set. Everything was too fast.

"I didn't get scared about the first set, because I knew I have a better level, and I can play better if I stay there and I really started moving better and hitting the ball stronger.

"So after the first set, I got fire inside myself, and I said that now I start the match. So it was much better. Game by game, I felt that my level is growing, and I had more confidence to go through it."

Halep went into the first grand slam of the year without a coach and with just one competitive match under her belt after recovering from a back injury, so the French Open champion took the positives from the tournament.

Asked what she could take out of her four matches, Halep said: "Close to 10.

"I have the courage to say that, because I took the risk to stay home so much, and I haven't been prepared for the highest level in tennis, but I did not play bad, I'm happy about the way that it's been going this tournament, and I take only the positives. I had great matches. I had the toughest draw, but it was nice."

Halep confirmed she has held talks with coach Thierry Van Cleemput after his split with David Goffin, but said she has not appointed the Belgian - who was involved in her warm-up routine.