He took command early in the second set before Lapthorne finally got on the scoreboard although it proved not enough to halt the run of his opponent.
"I have to find a way to talk to her so she can play her best".
Popular Halep's simply overpowered Williams, the tournament ace leader, and peppered her with an wonderful series of shots that wowed the crowd.
"She really played out of her mind", Williams said.
"I have always been intimidated a little bit when I faced Serena", admitted 27-year-old Halep.
She also revealed she has been trying to get into the mindset that has made her the most dominant player of her generation.
Williams started the match on the world's most famous court with an ace but was broken to 30 in the opening game.
Serena sprayed a forehand error in the first game of the match to give serve away, finding herself 2-0 down when Simona held at love in game two with a backhand error and allowing the Romanian to grab another break with a backhand down the line victor.
Serena Williams delivered a stinging rebuke to fellow tennis legend Billie Jean King who said she should focus on tennis and stop behaving like a celebrity and fighting for equality.
Self-doubt began to erode Williams' confidence as Halep took the set in 26 minutes.
Music superstar Niall Horan even had his say claiming that her interview was his favourite part.
"It feels good", was the first thing she said when she walked into her news conference pointing at the purple-and-white round badge.
Ex-American player Tracy Austin said everyone was "stunned".
Halep won 14 of the first 18 points, with many in the crowd roaring for each of the rare ones that went Williams' way. "If he's on it like that and I'm not, that's what happens".
"It's something very special and I'll never forget this day. She's an inspiration for everyone and the model for everyone", Halep said.
"I had nerves. My stomach was not very well before the match but I knew that there is no time for emotions". I respect a lot what she has done and what she's doing. "Yeah, I feel really calm about it". When I started the tournament, I talked to the people from the locker room that my dream is to become a member here. It's not like I'm happy to be in the finals, and it's Serena and there's no chance.
She didn't merely play defense, though, managing to go from retrieving an apparent point-ending stroke by Williams to lashing a victor of her own in a blink.