Police said Sunday they were investigating the death as a homicide.
The 34-year-old jockey was found by a family member late Saturday night, police Lt. Richard Sandoval said.
A 911 call was made about 11 p.m. and the caller said a man was "lying inside the house, who may possibly be dead," police said in a statement.
Paramedics told police the circumstances appeared suspicious. Antley was pronounced dead at the scene with "severe trauma to the head," the statement said. An autopsy will be conducted by the Los Angeles County Coroner's Office.
No arrests have been made.
A friend of Antley's had gone to the airport to pick up the jockey's brother, and when they returned there was no answer at the door, according to Ron Anderson, Antley's former agent. "There seems to have been some struggle at the house," Anderson said.
Gary Stevens, a fellow rider and longtime friend who spoke Sunday with Antley's wife, Natalie, said he had been told it appeared the jockey was struck in the back of the head.
"He seemed to have some fear that something like this was going to happen," said Stevens, who last spoke to Antley three weeks ago. "A lot of things he was saying were not making sense to me.
"I love Chris as a person and all I can say is that mentally he was just having a tough time. He had a lot of demons haunting him."
Natalie Antley, who is expecting the couple's first child, was in New York at the time of his death, Stevens said. The Antleys married earlier this year.
The driveway of their home was blocked with yellow police tape; a bouquet of pink and white roses rested against a black iron gate.
Detectives combed the front yard of Antley's house, going through papers in a trash can and examining a window to the right of the front door.
Jim Herzfeld, who lives next door on the cul-de-sac street near the Rose Bowl, had been friendly with Antley since the jockey moved in about 18 months ago.
"It's sad," Herzfeld said. "We had hopes that he would get back on track."
A moment of silence was observed and flags were lowered at Hollywood Park in Inglewood.
"He was just a tremendous athlete and when he showed up to do his job he was one of the best in the world at it," Garrett Gomez told KABC-TV in Los Angeles.
Antley's career was marked by frequent battles with his weight, alcohol and drugs. He lost his New York jockey's license in 1988, when he tested positive for cocaine and marijuana.
After entering drug rehab, he came back to win his first Kentucky Derby aboard Strike the Gold in 1991, then won the Derby and Preakness with Charismatic in 1999.
Antley stopped riding in March because of his balloning weight, which the 5-foot-3 rider had tried to fight over the years with diet pills, fad diets and self-induced vomiting.
He finished second in his final race at Santa Anita on March 19.
"I know he had his problems, but he was a good kid," Anderson said. "He was a very kind and generous person."
Last year, Antley made yet another successful comeback from struggles with weight and depression to ride Charismatic, a lightly regarded 3-year-old. They missed winning the Triple Crown when the horse finished third in the Belmont Stakes, then pulled up just past the finish line with a broken leg.
Antley jumped off and immediately held the colt's leg until veterinarians arrived.
"He instinctively came to the aid of the horse. It was a very heroic and admirable circumstance," said Bob Lewis, who, along with his wife, Beverly, owned Charismatic.
Lewis said Charismatic might not have been saved without Antley's quick intervention. The injury ended Charismatic's racing career, but the horse is at stud in Kentucky.
"We just thought so highly of Chris," Lewis said.
Trainer D. Wayne Lukas paired Antley with Charismatic and called the jockey "a very, very talented rider."
"When I think of Chris, I remember that he found himself in the right place at the right time and on the right horse," Lukas said. "I'm so glad that he had that opportunity to once more feel that thrill in his lifetime of winning America's ultimate race."
Lukas said he was surprised that Antley, whom he described as "a very likable guy," didn't continue riding this year.
"He had some personal problems that, I'm sure, were disruptive in his life," Lukas said. "But it certainly seemed he was headed in the right direction."
Antley began his career in New York, and was the nation's leading rider in 1985 with 469 wins. He was the first jockey to win nine races in a single day, accomplishing that on Oct. 31, 1987, with mounts at Aqueduct and the Meadowlands.
He moved to Southern California in the 1990s. He won 3,480 career races from 19,719 mounts, and his horses earned more than $92 million.
©2000 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed